Ignition noise that has me baffled.

Greetings all-

Okay… I’ve read almost every post here I could find on noise/grounding, and I’m stumped on this one: Upon completing my install, I have ignition noise in both highs and subs. It happens in ACC and ignition mode, regardless of the engine running or not (and does NOT change with engine running). It does NOT change pitch with RPMs. It sounds like electronic wind that starts low, gets high, back to low, slowly reaches high, etc. No crackles or pops.

My setup:
2004 Chevrolet Trailblazer LT, with Onstar, No bose
Kenwood Z828 HU (4v preouts)
JL Audio 300/2 on highs – JL Audio XR 650 CSI 6.5 components in front (no rear channel)
JL Audio 500/1 on subs – 2 JL Audio 12w3s
Stinger blue colored RCAs (directional, already checked that arrows are pointing towards amps), one on front, one on non-fading
4 gauge from battery to 125a Stinger fuse under hood, then to fused distro block in back, then 8 gauge to amps
8 gauge ground @ .7 resistance to amps
Power wires & RCAs/speaker wires on opposite sides of car
PAC OS-2 (keep Onstar interface/wiring harness)
PAC SWI-X Steering wheel controls interface
Kenwood Sirius tuner (1st generation, cant remember model #)

What makes noise go away by about 97%:
1) Disconnecting RCAs @ amp side
2) Disconnecting RCAs @ HU side

What does NOT make noise go away / things I’ve already tried:
1) Disconnecting antennae
2) Disconnecting sat tuner from HU
3) Powering up HU w/out sat tuner and SWI-X (see 6 below)
4) Moving crossovers around (passive crossovers part of component kit)
5) Using jumper RCAs, avoiding everything electrical I can, from HU to amps
6) Using jumper wires on ACC, 12+ constant and ground for HU. (Initially the HU, sat tuner and SWI-X were all connected together off the OS-2 harness for power and ground. I removed the HU from this and jumpered to alternate power source (ground and + under rear seat – fuse box. No difference).

What I haven’t tried:
1) Removing the screws that mount the amps; they are attached to the back of the rear seats, which I suppose are somewhat/fully grounded to the frame. I didn’t think this would matter since the noise stops when I remove the RCAs, but that’s why I’m asking.
2) Something I haven’t read about or missing.

What’s weird:
After the troubleshooting listed above, I assumed my deck was the problem. After cussing for a few minutes, I drug a boombox into the garage, set it to AUX input, jumpered the front out from HU using RCAs to the aux in on the boombox, and got NO noise. I turned the volume up on the HU and heard static (had it on no channel on radio) to verify the setup was working. But there was NO noise.

So at this point I’m baffled. I am hoping someone can point out something I’m missing, and make sense as to why this is happening, or at least give me some direction. The noise isn’t terribly loud, but you will hear it when its quiet in the car (like @ night, especially when changing tracks or during silent parts of music.)

I’m hoping to eliminate it, because I did a lot of reading here before doing my install, and I took my time doing a very clean install, and now very disappointed with the noise. Any help will be greatly, greatly appreciated. Thanks.

Update: I found that by removing the turn on 12+ (effectively turning off) the sub amp, the noise goes away.    The only thing _I_ can think of is the RCAs are too close to the power cables of the nearby amp.

I am going to play with wiring positions and post an update. If that doesnt fix it, then I'm stuck again.

Okay, at this point, I am reasonably confident that it is a grounding issue.

When I jumper the ground of the sub amp w/a ~20ft 8 gauge cable to the battery, the noise is noticeably worse.

FYI - both amps are grounded at the same spot - bolted underneath the back seat anchor. I know a lot of people say this is not a good ground, but I figured with .7 resistance, I was good, but perhaps not?

I suppose at this point the next step is to use another ground. Scrape paint away to bare metal and try that. Opinions anyone? And does the length of the ground matter? They are probably around 3.5 feet or so. This seems to be a very opinionated question.

Thanks.

Have you tried a ground loop isolator on those RCAs.  Those work well with the type of noise you are describing and they only cost like $15 at your local shop.

No, I haven't tried an isolator. Don't you lose SQ when you use those?

I moved the amp grounds to a new location - scraped paint away and used a gold grounding plug. I still get the same noise, so I'm stumped again.

If the noise occurs with the engine off it is not engine noise.  Problems like you describe are almost always ground related, but it can be defective head unit or RCA cables or a bad level setting.  You tried new RCA cables run using a different route?  Have you tried moving the amps?  Have you tried unmounting the amps and isolating them from the vehicle completely?  Is the noise from one channel or one amp and not present in others, or is it uniform everywhere?  If it is isolated, can you make the noise "move" to other amps?  If it is everywhere try splitting the amp grounds to two different locations and see if it changes then.  Have you tried a dedicated ground for yout HU (not using the factory ground?)  Have you tried unmounting the HU?  Have you tried grounding the case of the HU?  Have you tried grounding the outer ring of the RCAs?  I cannot recomend a ground loop isolator as that only masks the problem it does not solve it, and you have more work to do to isolate the source it seems.

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When you unplugged the RCAs at the HU and the amps and got the same result ( 97% gone ) this would indicate it is NOT the RCAs. If it was the results would have differed. I would look at the grounds. Get away from the seat bolt ground. Scrape the floor bare. Try a thru bolt.

i figured it out. it was a high/low signal source switch on the amp. (high accepting 200mv-2v preouts, high using 2v-8v.)

i reversed the setting and the noise went away. i then set the levels on the amps using a DMM described on jls site, and everything sounds golden. no hiss, no noises, no turn on/off thumps, etc. just great sound.

after the level adjustments using a DMM, i now have to move the non-fading output (connected to the subs) on the HU to balance the stereo.

im going to get with a friend to do some more sound tweaking, as well as start understanding the whole System Q thing to get the most out of my system.

many thanks to those who replied.