This is in my brother's Altima.

Over the weekend we tried to amplify the interior speakers. We bridged the amp to get the most power out of it. The rca cables from the rear output on the deck [Pioneer DEH-7600] and the output speaker wires from the amp going to the speakers are run along the driver side of the car. The power wire and remote turn on are run parallel along the passenger side. The amp is located in the trunk, grounded to bare metal. I did notice when I first started the car, I heard some squealing noises, possible from the alternator belt?

Problem:

When the ignition is in the accessory 1 position, the speakers play CRISP.
When the ignition is turned to the "ON" position, there is a whining noise being emitted thru the speakers. When the car is started, the whining gets louder and follows the input on the gas pedal.

Ive concluded its alternator whine.

Attempted solutions:

I've pulled out the rca cable on the amp and the whining went away. I connected a spare rca cable to one side of the input and the whining was not present.

I've switched the crossover from High Pass to Low Pass and the whining went away but, as soon as I go back to high pass, it comes back.

I've switched amps, tried using different RCA cables, tried different ground points the whining is still present.

I've tried turning the gain on the amp down to about halfway point but, the whining continues, just not as loud.

Possible Solution:

I've read online about the ground loop isolator but, some say its not a solution to the problem, its just masking it. I want to solve the problem [if possible].

Heh Im just frustrated with the stupid thing, I just unplugged the power wires

I have this problem in my 240. Okay. Re-Ground the amp, make sure it's got bare metal to metal contact, and that the cable is of sufficient gauge. Next, get a quality pair of shielded RCA's. If that's not it, If it's a Pioneer headunit ground the RCA outputs on the headunit to the headunit chassis. If you still have a problem, try running the wires down opposite sides of the car, power on one, RCA's on the other.
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Attempted solutions:

I've pulled out the rca cable on the amp and the whining went away. I connected a spare rca cable to one side of the input and the whining was not present.
-That's because you had to signal for the amp to play. So that's why no whining.

I've switched the crossover from High Pass to Low Pass and the whining went away but, as soon as I go back to high pass, it comes back.
-Ground loops usually only effect high signals, I've heard of them distorting subs, but not too common.

I've switched amps, tried using different RCA cables, tried different ground points the whining is still present.
-Hm. Pioneer headunit?

I've tried turning the gain on the amp down to about halfway point but, the whining continues, just not as loud.
-Still getting the signal, so yeah. The problem will continue.

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http://www.caraudio.com/forum/showthread.php?t=198477

That has all the answers you need.

thats for the help nismo. There is one thing that I seemed to have overlooked. The remote turn on is running on the same side as the power wire. A few people have said I should have put the remote turn on on the side with the audio cable as the power wire will tend to cause interference on the turn on wire.

Wow, this thread helps a lot. I have an engine noise problem as well in my B14. I have a Pioneer head unit also, so that might have to be checked. Now that I have read this, I think I am running my power wire and my RCA cables on the same side. I'll probably go out today and switch one of them over to the other side, and see if my engine noise goes away. It is really annoying, and especially when you accelerate. Hopefully one of those advices work...

Wow, this thread helps a lot. I have an engine noise problem as well in my B14. I have a Pioneer head unit also, so that might have to be checked. Now that I have read this, I think I am running my power wire and my RCA cables on the same side. I'll probably go out today and switch one of them over to the other side, and see if my engine noise goes away. It is really annoying, and especially when you accelerate. Hopefully one of those advices work...

I found thru some more searching on the net that its probably the pioneer headunits. after a while, the internal rca ground can short out or some nonsense causing the feedback.

here is a post I made on another forum with the info on how to correct it. I didnt get a chance to do it to mine yet so I dont know if it actually works. Others swear by it!

http://forums.nycmaximas.org/showthread.php?t=26833

yeah its a bad ground, reground the head unit. That should fix your problem.

add an extra wire to your head unit ground and ground it in two places, make sure at least one ground is on bare metal. you can touch around with the wire while the radio is playing to see when the whine goes away