H964

hi guys,
i am back in a 964 after 2 years of missing out. i found the perfect car and couldnt be happier. sorry no pictures yet, but coming soon.
i noticed recently that i hear a humming noise as i accelerate, stops when i turn off the stereo.
any ideas?
also ,looking for the following parts:
1- a suspension set up and h&R green springs
2- 17 wheels
3- rear spoiler motor cover
4- black shifter cover or something nice
5- clear lenses
6- vents to replace fog lights
7- cdr 210

i know i am asking for many desirable parts, and most likely everyone else is looking for them as well....... oh well ,worth a try
good to be back

groovzilla

are you sure the noise stops when you turn off the stereo because most humming noises are caused by clogged fuel filter or fuel pump going bad.

H964

pretty sure its the stereo, as it clearly stops when off.

stinkydog

My radio does the same thing. The explanation I've seen is RF interference from the dual ignition system... makes sense, since the sound changes in frequency/pitch as RPMs change.

-nick

I've got a slight hum / whine through the speakers too. Can you hear the pitch change with rpm? - mine does.

My next stop is to spritz the ignition wires with water in the dark to look for arcing. Otherwise, I'm not sure what to go after.

BlueHeeler

It is probably one of 3 things:

1. Bad ground between the radio and car. The radio source has a ground loop. If it is an aftermarket radio check this first.
2. Interference from the ignition. This could be caused by a faulty ignition wire or a bad/loose connection between the plug and boot.
3. It could be alternator whine if the alternator is on the way out. Check this last.

I am not sure of the audio system in the car, but I think I read there is a factory amp. I would start with the simple things first.

-nick

Thanks Blue,
I've got a CDR-220 plugged into the factory harness for 12v and ground. Also an aftermarket amp under the seat that gets 12v from the stock amp harness and is grounded to the grounding stud under the seat. I've had a few different amps give the same whine so I think I can rule it out.

This gives me a few things to check -

1. Replace the factory stereo ground and try a wire directly to a nearby ground point.
2. Spritz the ignition wires to check for arcing.
3. Oh crap, I hope it isn't the alt

The whine is only noticeable with the volume all the way down and the head unit "on" (and windows up), so it isn't enough to annoy me into a frenzy.

BlueHeeler

Good luck. Finding the problem is usually not mechanically difficult, but potentially time consuming.

Although not pcar specific, here is a pretty good article explaining the basics
http://www.termpro.com/articles/noise.html

wellcraft290

definately a ground and usually off the alternator. happens on any car not just 911's

Streetfighter

No reason to turn on that radio! Lol.