constant hum from rear speakers

Hey guys, I have tinkered with my new system for days and am still cannot rid my self of a problem. On my HU (Pioneer DEH-7300BT) I have front and rear/subwoofer switchable RCA outputs. I have an RCAs running from both of these to my amp (Infinity 475a). When I turn the key, even without starting up I get a constant from only my rear speakers. I have switched my RCAs in every way possible with the same results. I have also tried the trick of grounding the RCA at the HU with a wire leading to ground. When I did this, no matter which RCA I grounded the humming stopped, but so did music on the rear speakers... I tried the same thing on the amp side but it only made the hum worse. When I hook my RCA from the front output on the HU to the rear input on the amp the rear speakers work great and there is no hum. But then if I try to add the rear HU outputs to the front input on the amp the hum returns, but still only hums out the rear speakers!!! What the hell is going on here. My fronts speakers never have issues and my sub is always fine too... (it is hooked up to RCA outputs on the amp). I also get alternator whine, but it is only apparent whenever the hum is present. If I have the front HU outputs hooked either to the front or rear amp inputs it is always clear, even with engine on. The problem always comes when I hook into those damn rear/sub HU outputs. There is a picture of my HU below. To be clear, both RCAs I have are plugged into one white and one red and match the same with the amp. I really tried everything to figure this one out on my own, but I need some help. THANKS IN ADVANCE!!!

TYPO: When I turn the key, even without starting up I get a constant **HUM** from only my rear speakers.

Defective HU, RCA cables or amp, or amp gain too high or speaker impedance too low.  But if you connected the rear channel of the amp using the rear RCAs to the front output and no hum, I'd say defective head unit.  Is it under warranty?Support the12volt.com

 2 things.....What is the R/SW rca output set to in the menu Rear or Sub?

If you have swapped RCAs and the result of it all is always rear speaker "hum", then try to swap the front speakers to the rear channel and rears to the front and see if the hum moves to the front speakers. If so, the amp is either not setup properly or its bad

i am an idiot wrote: http://bcae1.com/images/rca/temporaryrcashieldrepair.html

Hey, thanks for the tip... I actually came across the same site lol. Anyway, this method did not work for me, but I found something that did. Because my front outputs were working fine I just put Y-cables at the end going into the amp so that the front output runs to both front and rear speakers. I dont know if this makes the quality any less but sounds great to me???? I then hooked my rear/subwoofer outputs directly into my sub amp inputs instead of running first to the rears through my 4 channel amp and out the "aux out" to the sub amp. This seems to do the trick, my speakers and subs sound crystal clear, fully powered and there is not engine noise. Will using my front outputs on both front and rear speakers have any negative impact on my system?? I figure my amp has separate gains and frequency adjustments for the front and rear so I should still be able to customize my sound, I will only loose the ability to make some fade/balance adjustments from the HU which is no biggie. Am I correct? I mean, like I said it sounds great, but if it could be better I would love to know... Thanks a lot for your replies guys!!!!

Oh one more thing? Anyone know why my rear/sub outputs work great to the subwoofer, but not to my speakers? Is it because the higher frequencies are filtered out through the amp??? Thanks

The r/sw output is either or.  It is switched in the radio menu.  Rear sp full, or sw.  Set it to full, use the output from your 4 channel, turn the crossover on the sub amp on and adjust.

From your original post, you said the little ground wire to the rca's stopped the hum.  This sounds like you blew the protection fuse on the sw output of your deck.  This usually happens when your amp is not properly grounded and the amp trys to get its ground through the rca's.  This is an internal problem in the radio now.  You could have it fixed most likley free, if it is under warranty, or live with it the way you wired it with the "y" adaptors.