jmporsche944

Well, what I thought to be a whine coming from the drivetrain ended up only being feedback through my stereo. What would cause the stereo to produce a high pitch whine that increases with rpm? I have a pioneer headunit, amp and subs if that makes any difference. Could it have anything to do with the amp being mounted right onto the body? TIA

Jeff

89AZ944

Here's a couple of things-

Improper grounding is one thing to look for. Increasing whine with RPM points to RF interference from the the distributor/spark plug wires. One other thing to look for if the noise is only coming out of one speaker, the length of the wire going to that speaker could be the perfect length to catch RF from the engine. Attaching a small extra length (6-8 inches) to the wire takes care of the problem. Mounting the amp direct should not affect anything unless the manual for the amp specifically says not to do it. I can't think of one off the top of my head that does, but it has been a few years since I have worked with sound equipment......

89AZ944

Cracked rotor housing on my old nissan truck made the radio have a purrrrrrrrrr noise that changed as I revved the engine........

KuHL 951

I had to take off my rear wiper because of the worst interference I've ever heard. It sounded like a jet taking off and did it even when the stereo was off and the wiper was on(Blaupunkt's are always on and can be used without the key 'on'). I swapped another motor out and it did the same thing. Both of my amps are mounted behind the rear seat. Oh well it doesn't rain out here that much. I figured it was the long path to a body ground that the rear wiper has.

Charlotte944

Alternator whine.

Alternators put out AC (Alternating Current), which is then rectified to DC (Direct Current). However, the DC voltage has a small amount of AC "ripple". Typically the ripple will be shunted to ground via a capacitor (Capacitors BLOCK DC and PASS AC). If the noise supression cap at the alternator is bad, you will have the whine.

Additonally, adding external amps to an already noisy electrical system will cause the amps to amplify the ripple.

Go to you local auto stereo installer and ask for a noise supression "kit". You should get a choke (inductor) and a cap. The choke goes in series with +12 volts, and the cap goes across +12 volts and ground. This forms an 'L' type band-pass filter. The choke supresses changes in current flow and the cap shunts any remaining ripple to ground.

jmporsche944

What you guys are saying is making perfect sense, but, it did not happen until i remounted my amp to the body in the rear. I guess ill just try installing something between the amp and body and see if that works first. Thanks.

Charlotte944

I'd wager that you were getting some capacitive filtering before you hard mounted the amp. Just put a cap across +12 volts and the amp chassis ground point.

Judson951

I think that was the cat under your hood.

89AZ944

I wondered why that thing ignored me so much.....