volume drop after ~15 minutes , no sub

Sorry for the long post, but would really appreciate opinions and guidance. My setup I started with: Kenwood KDC-BT945U (bought off ebay as mfr refurb) Polk Audio DB571 front (100W rms max, 4ohm) Polk Audio DB691 rear (100W rms max, 4ohm) Factory HU speaker/power wire. Setup/install went without issue. Have installed 10+ HU's over the years. Blue-tooth works great, USB jump drive works great, sound quality is phenomenal. Running at 70mph with the windows down requires a decent amount of volume to get sound worth listening too. I listen to a lot of metal (ozzy, metallica, puddle of mud...), so the louder the better. After about 10 minutes or so of running at 25/35 (USB as source), the volume drops dramatically and crackles. I turned it down for a minute, rolled up the windows, turned it back up to 22 and it was all good. Bumped it up to 25 again and it dropped the volume again within a few minutes. Bought an amp: Kenwood 4 channel amp KAC-9452 (70w rms x 4 @ 4 ohms) - HU amp off - kicker 4G install kit with twisted pair RCA's to the trunk Figured I needed an amp to push the polks. Had best buy install it with a kicker AWG 4 power wire and twisted pair RCA's along with a 3rd set of RCA's in case I wanted to throw in a sub later. I haven't run an amp since I was a teen (15 years ago or so), so I figured I'd let someone else deal with crawling around and installing stuff. Did what appeared to be a great job with the install, also ran new heavy wire to the front doors and rear deck for the speakers. Readjusted all the EQ settings and whatnot on the HU, shut off the internal amp, turned the low end boost off on the HU, adjusted the low end of the EQ to sound good when loud so I could bump it up when I have the volume down and windows up. Pounds hard, sounds awesome after some further tweaking of the EQ. The amp has the boost shut off and is set as high pass on all 4 channels, with the gains at about 50%. Rolling along after the install (first hour long commute after install of amp), volume at 30, sounds great severly better overall than when using the HU alone, bass hitting hard, vocals sound like I'm at a concert (deafining levels)... volume drops out... So... Love the features, used to the features (playlists are a must), have run kenwood HU's for years... contemplating setting it on fire. As far as my issue, since I bought my stuff on ebay, I can't really send any of it in to get it fixed without paying a premium I'm sure. Considering what I spent on the HU and amp, I'm not out a lot. The installation fee for the amp (labor and all wiring, 4 gauge power, 3 rca pairs) cost as much as the HU/amp combined! lol ($216 install, $225 HU/amp via ebay) I have yet to come across anyone that has my issue when using only the preouts and the internal amp off in the HU. Everyone I've come across that were having issues were using the internal amp. Even still, I ran across a few posts on various forums where power to the amp was the issue. So, I started to look at my wires in the trunk. Upon checking the ground connection that the installer made, I realized he used a self tap screw into the thinnest piece of metal back there. The screw also would not tighten as it seemed stripped. So, bad connection number 1. Since I don't have hardly any spare wire (about 2 feet of ground/3 feet of hot from the kicker install kit the best buy guy used), I had to find somewhere that was at least double thickness tin to screw it to. After wigging things around a bit, the hot terminal end came off the cable tied to the amp. Upon further inspection, I noticed they did not solder the terminals on the ends of the power or ground wire, they were just crimped, and obviously not very well. So, I pulled the ends off the ground and hot, put a new ends on the longer piece of ground I had so I could reach somewhere useful/thicker metal. I then used a heavy 1/2" bolt/nut (vs self tap) through a double thick support in my trunk for my ground. Bad connections 2,3 and 4 resolved. When unscrewing the terminals from teh amp, I also realized that both hot/ground were not tight. Bad connections 5 and 6 resolved. So, basically, my entire power source was poorly connected and poorly grounded. Took it for a drive (hour commute), wasn't a bad power connection at the amp... volume still drops on it's own when ran for 15 minutes or so at high volume. Tried to rule out the HU today. I disconnected the HU and connected a mp3 player to my amp using splitters so I could drive all 4 channels. After about 15 minutes, the volume drop happened again repeatedly just like it did with the HU driving the amp. So, since my issues first presented with only the HU and speakers (no amp), do I then assume that the speakers are doing something wonky? Like changing ohms on me as they heat up after some use? I could see that causing a volume drop... A short would obviously drop the sound, but would drop it completely in a channel, in my case, all 4 drop similarly as far as my ears can pick up. Not a specific frequency, just the volume seeming to go down. Or, do I just assume that kenwood's amps aren't able to supply enough power (unless I drop more cash on their excelon series) or find one of their others that puts out more than the one I have... This is a very strange problem to me. What makes it more strange, with just the HU, the speakers would go loud, then the volume would drop and crackle badly. With the external amp, the speakers don't crackle at all, only a volume drop. If I turn the HU up further (with the amp), they get as loud as they were before, or pretty close regarding where I have my gains on the amp now set. There is a fine line where it just constantly fluctuates. If I keep it couple ticks below where it drops, it will run like that for over an hour without any issues. If I turn it up a couple ticks to the point where it drops, it fluctuates up and down about the equivalent to 7-8 ticks on the volume knob. If it drops and I jack the volume up beyond the fluctuation point, it will run loud and not drop out on me, but is about 7-8 ticks higher than where the same output volume was before it dropped down. Now, in hindsight, if I paid retail for this stuff, I'd be livid due to the cost/performance. However... if I paid retail for this stuff, I'd be returning it. At least I ruled out the HU... I really like this model as it seems kenwood dropped streaming BT from their newer models due to complaints of poor audio quality. Personally, I like being able to stream talk radio over my phone to my HU... so the sound quality isn't an issue. Anyway, it seems not many people have my issue or know a resolution. Or I just can put the right wording in a search to find something similar. Right now, I'm thinking of picking up an amp that I can find decent reviews on that isn't kenwood and giving it a try... Would be nice to know that is my issue before I spend the $. Any help or suggestions would be greatly appreciated.

Sorry, can't edit the post. Car: 2007, Mercury Grand Marquis. Factory battery. Factory alternator. All other pertinent info is in the first post regarding the audio system I have.

ok, lets start on your perception that your ground needs to be on thick metal. not exactly true sir, your ground should be as short as possible from the amp and it only needs to be screwed to bare unpainted metal, if its not then your ground could still be a problem.

second problem you have already mentioned, the speakers could just be getting hot after a while and presenting a low ohm load to the amp and making it act funny.

you could try making a new fresh ground for the radio also to bare metal because sometimes factory grounds just arent good enough to run anything aftermarket.

another thing you can do is put the volume on your head unit to below where you start having symptoms and then raise your gain on the amp a little bit to compensate. if you still have issues then i would rule out your radio as being the problem and look more at your wiring and speakers.

Thanks for the tips. However, I ruled out the hu by using a portable mp3 player directly to the amp. So I don't think the hu ground or hu is a factor. The ground to the amp is about 18 inches, 4 gauge. I'll debolt it and make sure I sanded the paint away, which I think I did... But it was getting late at night and I may not have. The speaker wire is 16 gauge, kicker brand using wide/narrow spade connectors to the speakers. I had failed to mention that I maxxed the amp gain before I did anything at all and it just caused the problem at a lower hu volume level. I only used the portable mp3 to further rule out the hu as my issue. Will take a looked.at the ground today and may also run a volt meter to my battery to see if it's dipping a lot when I turn up the volume. Thanks for taking the time to go through my post.

Shoot, I did forget to mention that when running it hard yesterday I noticed that the 6x9 speaker magnet/disk holding it on does get pretty warm to the touch (probably 80F+). My amp gets fairly hot to the touch in one area (would guess 130F+). didn't have my IR thermometer with me... will take it when I fuss with the ground and retest. I run RC vehicles, so I deal with hot engines/electronics quite a bit and use my IR therm for those constantly to monitor engine tune and whatnot.

man this is a tough one to figure out without actually being there to seem exactly what it does and when. this really sounds like you have a speaker that might be temporarily grounding itself to metal or it could be a damaged speaker, or possibly when the speaker was screwed in it warped the basket which could cause a coil to contact the magnet but still play fine at lower volumes. whatever it is, it probably wont be something obvious.  if you have a multi meter you can test the speakers for the propper ohm load and i would push on the cones to make sure it travels good and nothing is grinding against the magnets.

you could also have a pinched wire thats partially cut and creating a bottle neck and making the amp have to work harder than it can sustain.

I'm kind of thinking it's one of my 6x9's in the rear deck. When I fade to that speaker alone, it doesn't sound as good as the opposing speaker. Seems to distort a bit easier. Since fall/winter is on it's way, I'll be running with windows up, so volume won't be such an issue as it definitely goes plenty loud with windows up. I may revisit this next spring when window down running is more how I roll. Or, if the speaker dies on me... then will be an obvious fix.

A shorted speaker could easily take out a radio or an amplifier.  I would do some more research to see if you may have a shorted driver on that speaker.

Now looking for a replacement amp. After doing some digging, I found that quite a few people experienced what I have with various kenwood amps. From what I've read, it's essentially thermal shutdown, just not all the way off. Now, trying to find a decent 4 channel with 100w rms per channel.

that might be the obvious sign of what the problem is but if there is something wrong that is causing the amp to go into thermal protect then it might do the same thing with a new amp. all im saying is that if you aren't sure that it's just a defective amp then you need to keep investigating the install. ive seen a lot of people waste a lot of money because they didnt look close enough at the install and then just go out and buy new equipment only to have the same things start to happen. not trying to discourage you or anything like that, its just words of wisdom.