I have noticed a hiss in my passenger side rear 6x9. The hiss does not appear to change volume when the volume of the head unit is changed, and is only present when some other part of the electrical system is on (A/C, headligths, fog lights, etc). It does get lounder immediately after I cut the ignition for a brief period while the other car electronics are powering down (this is actually the only time that I notice it). It does not appear to come from the head unit, RCA's, or the speaker (I just replaced the latter two).
The amp that runs the 6x9 gets power from a fused distribution block, along with another amp, and both amps are grounded via a common ground wire and a grounding block.
I would think the amp is defective, but the hiss goes away when the other car electronics are off (or else it is there, but inaudible). With all the other car electronics off (except the car stereo stuff - head unit set to zero volume), I can flick fog lights on and off and hear the hiss get louder and then quiet down, respectively. Because of this, I can only think that somehow the ground isn't good, but I wanted to ask the question before I go digging around and re-routing the ground.
Any suggestions?

You mentioned that your replaced the RCAs. Did you run them in the same spot as the old ones? For the hell of it, try running them temporarily right down the center of the car and see what happens.

I will play with the RCA's again when I get a chance. Running a test set down the middle of the car is a good idea (since I have an extra pair).
Do you know if there is something that creates interference under the passenger side dash. That's the only place I can think of that could be problem. It's just strange because I have both pairs of RCA's running right next to each other and there are no problems in the other speakers.

Is there a good program to use so I can draw a wiring diagram? Maybe that will help. I could be committing electrical sin and not be aware.

Powerpoint perhaps?

Well, it worked, but it was a big pain in the butt making all the lines. I'm glad I used colors for different types of wire to make it less confusing. Saving it as a .jpeg was easy under the "Save As" function. Here it is:

How did you rule out the HU? A good quick test would be to switch the right/left RCA out at the HU and see if it switches sides. The only reason I’m back at the HU is because I have seen The EVTC (Electronic Tone and Volume Control) IC’s get noisy on one channel before. But I’ve also seen the Pre-Amp IC’s in amps get noisy as well. Either of these problems could cause what you’re seeing and a quick right left swoop could rule one or the other. Swooping around RCAs at the amps to could help rule them out as the place the noise is coming from.

Thanks for the suggestions. I will check these when the SNOW quits falling It was 70 degrees on Wednesday....
I actually did try swapping the RCA's at the amp, but it was before I put in my new Infinity's - the hiss actually seemed louder with my old Pioneer 6x9, and I traded out one of the RCA's for a twisted pair (I think this may be part of the reason it got quieter, and leads me to believe there is some kind of external interference). Since I have made all these changes, I should probably check everything all over. I will try these things.

1. Switch RCA's at the amps (left for right and front for rear).
2. Power the speaker with the other amp.
3. Run an RCA down the middle of the car.

Crutchfield has a pretty good website on this, although it's not nearly loud enough to pay for those noise suppressors.
http://www.crutchfieldadvisor.com/S-...de.html?page=3
http://www.crutchfieldadvisor.com/S-..._diagnose.html


I should be able to low-pass the speaker at around 100hz and remove the hiss that way if there is interference coming from anywhere except the amp or the speaker wire, right?

Your wiring looks fine, although typically a block diagram of your wiring isn't going to provide a lot of insight into where the noise may be coming from.

I would try a few things. Start with moving the physical location of the RCAs to see what effect that has. If it has no effect, then start fooling with grounds. Wherever you grounded the amps to chassis, ensure that the chassis is scraped clean to bare metal. I also prefer to use a star washer that bites into the metal. When grounding to tin panels (like you pretty much have to in a thirdgen), I prefer to drill a hole and use a nut & bolt instead of just using a self tapping screw. A little bit of di-electric grease on the ground helps keep out moisture and prevents rust and tarnishing.

I am slightly worried about the rusting, since the whole area could be rusted out by now.
Anyways, I fiddled around with it yesterday, and the noise seems to be gone now, but we shall see if it reappears. I switched the channels from amp 1 that were powering the sub to power the rear speakers, and amp 2 is now powering the sub. I should have done this a long time ago since it is a higher quality amp and likely achieves its RMS rating (250W RMS bridged - 30 amp fuse) as opposed to amp 1 (320W RMS bridged - 20 amp fuse - no way). The sub sounds a lot cleaner now. I'm still not exactly sure what the problem was, but that is how it goes sometimes....
Does anybody know of a noise that comes from the dash on the passenger side (not related to the sound system)? It is produced when I turn the car on, even if nothing else is on, and is actually more irritating than the speaker hiss. It has been there as far back as I can remember. What is under there?

The HVAC fan is the only moving item under the passenger side of the dash.

(Long shot) RFI from computer???

Since this is unrelated to car audio, I started a thread in the correct section here:

https://www.thirdgen.org/techbb2/sho...hreadid=288967