I recently had to replace my amp for my sound system in the Tracker. Why is another story, ( a dumb one.)  After install I noticed a distinct high pitched whine coming thru the system, and imeadiatly figured I had a ground issue with the amp somewhere. The noise sounded so much like ignition bleed I had no reason to question it, so I rechecked ALL my grounds, to no avail. The amp I used as a replacement was just one of those cheap auto zone/pep boys ones a buddy gave me, rated at about 350 watts, two channel, old amp was a 240 cheapo, which I did NOT get any noise from. Since I couldn't get the noise out with re-grounding I got one of those ground isolaters / noise reducers from Radio Shack, installed it inline from head unit to amp, still got plenty of noise. I have the amp set at max output, and I'll try turning it down a bit, but would still like to hear some suggestions for noise reduction.

how r the wires run?   are the RCA's run with the power wires?      that can make that sound

We had the same issue on a buddies 350Z.  We had to install an engine grounding kit that did a better job of grounding the engine and alternator.

Power for the amp is directly from the battery, via a fused HEAVY guage wire. Ground from amp goes directly to seat mount bolt, about 12 inches of HEAVY guage wire. The rca leads from the head unit are nowhere near the power wire. The amp does use a "remote" lead from the head unit so it turns on/off with the head unit.
Drone, what's an "engine grounding kit" and where would I get one? Thanks for the tips guys.

Check on eBay - several people sell kits that basically ground everything in sight to the same location, just a bunch of heavy cables really, but what they do is because everything is grounded to the same location, ground loops are eliminated.

A couple of things you could try.

First - disconnect the RCA input plugs from the amplifier and see if the whine disappears, if it does it's coming on the input lines, if it doesn't it's reaching the amp, either through the power or output wiring.

If it is the input lines try disconnecting the amp ground from the seat mount and wiring it back to the same location as the head unit ground - the idea is to eliminate a ground loop created between the power wiring grounds and the RCA grounds.

Yep, like fordem said.  You ground everything. 

Here is the example from the Z, to give you an idea of what was done on that vehicle.  Worked great, got rid of all the wine in the amp from the motor.

http://www.350z-tech.com/zwiki/Tutorial:Grounding_Kit_Installation

Got it. Pulled the seat, (amp is underneath) and went through each wire one by one, again. Found a small area where the power wire to the amp was rubbing through the outer cover, from the parking brake. Removed that section, as well as about 4 feet of extra, and reconnected it. I also took care to seperate the power wire from all other wires. Voila! Great Sounds again. I was able to remove the Radio Shack "ground loop isolater" as well . Now, Since this is only a 2 channel amp, "bridgeable" is it possible without f#*&ing it up again, to amplify the front 2 speakers? Right now it's only the 2 6x9's in the back. Granted it sounds kickin' but a more balanced sound would be nice too. I upgraded the fronts to some Pioneer 100w capable speakers a while back, but there only connected to the head unit directly. I dont want to mess up another amp.

Two channel "bridgeable" would translate to one channel with roughly quadruple the power when bridged, so I don't think you're going to be taking that route.

The big limitation in car audio is the "power supply" voltage, which is limited to 12V, and which limits the amp's output power.  There are different ways to deal with it, some amps have a DC-DC inverter section that boost the voltage supplied to the amp section, others use "bridging" which is essentially connecting the speaker across the output of both channels and then "inverting" one channel, effectively doubling the available output voltage and quadrupling the available power.

Well, that was a very thourough dissertation Fordem. I mean, Daaaammmmnnn! I'm glad somebody here knows there amp stuff! I've been schooled. For now I'll leave it as it is. It's already plenty loud enough, and the sound quality is quite good, rivaling or bettering many OEM systems I've heard. That in it self is pretty good considering the early to mid 90's Trackicks are about as acoustically sound as your average dumpster! Early on when I first got this trucklet, the noise inside at highway speeds reminded me of my army days flying left seat in small scout helicopter. Lets just say it was not quiet. In order to live with it I gutted the interior and Herculined the tub, sound and weather insulated all the panels I could get to including doors, rear quarters, rear deck, rear door, most of the floors. Inner rear panels have been replaced with 3/4 " finished hardwood, Kenwood 6x9's mounted to that. Insulated and sound deadened behind. That helped but it still ain't no Lexus and never will be. At least now the output level of the amp just slightly exceeds the ambient noise level at 70MPH. I can live with that.  Thanks all for the info and suggestions! And fordem, if your ever in the neighboorhood your welcome to drop by and check my wiring!

Sorry - was not my intent to offend.

A decade or two back I was into home HiFi and then did a bit of car audio - didn't take long to realise that getting gound sound in a car has it's own challenges, and then sort of lost interest when I discovered that what most folk were interested were so called SPL competitions, basically how much sound presssure could be generated with no real consideration for useability - either of the vehicle or the sound system.

And I'm pretty sure you'll be teaching me a thing or three in other areas 

  offend? I apologize bud, you misunderstood, I AM GRATEFUL! I meant everyword, your knowledge base is very welcome here, and your help is greatly appreciated! I sometimes just get too sarcastic for my own good, and it's hard to tell I'm trying to be humorous without seeing my face.  And, I meant it about the wiring, I can always use a knowledgeable 2nd opinion. Please, No offense taken or meant I'm sure. 

Thanks for clearing that up.