Constant humming when motor is running...

[pro-five-oh]

Hey all, my 95 LSC is giving me a few audio headaches. The first is this humming when the motor is running is bothering me. Its not in the spark plug wires, its a quiet hum that you hear at low volumes. See tech section for a list of what I have in this car, but its your standard 5 channel aftermarket system.

I have checked my ground to the amp, its nice and tight. The other end is bolted (sandwiched) between the rear seat crossmember and the chassis of the car, so that's gotta be good.

If it helps, the power wire is 4 gauge (fine thread) and the ground wire is also 4 gauge (I think) but its a coarse thread.

What do I do now???

[Steve Moran]

I wonder if it isn't coming from the alternator. I would give a try at poping off the belt and starting it up.
if this is the problem then I will bet it is the noise supresser in there. it looks like a condencer from an old points and condencer ignition system.
It is unlikely an autoparts store has then but it could be worth a look, Your best bet is to go to an auto electric store.

[pro-five-oh]

Steve, thanks for the tip.

This is one of those "lifetime warranty" alternators, and its about 4 months old. I am thinking I might have to swap it out for another one, might be a bad idea, I don't think its charging as well as it should.

[RJ Sclafani]

Did you find out what the problem was? Keep us updated on the situation.

[pro-five-oh]

Not yet. When I my stupid Midterms get over I'll probably go back to the parts store and ask for another one.

The alternator is putting out adequate voltage right now, so it will have to do. What a waste, I wish I could have bought a better one, but it was the only thing available at the time.

[RJ Sclafani]

How many amps is it running? What kind? How much is adequate? I have yet to look at any alternators. How big is the ground on the alternator?

[pro-five-oh]

Its the stock Mark VIII alternator, 120amps. Its a nice part, always worked fine on my 1993 model with the same stereo.

I need to run the car without the serpentine belt, but I am sure Steve's advice is right on the money.

Now to find the energy to complain about this new alternator (2nd one I have put in since I got it) again...

[RJ Sclafani]

geez, hope his fix helps you out. I would say to upgrade to a 130amp and try that out but you have a lifetime warranty.

[AceFrehley03]

Does the humming change pitch with the revolutions of the engine? I.E., can you hear the engine through the speakers, essentially?

If you can that means you need to check all of your grounds.

I had a 1977 Oldsmobile Delta 88 Royale (A.K.A. 'The Battletank') which had this problem on the original 6-speaker 8-track stereo system. There was actually a ground going into the head unit that I didn't know about which was causing my problem.

I know you said your ground was nice and tight... but check around, as there may be more then one. Just my $0.02. Good luck, sorry I wasn't more help.

[ March 03, 2004: Message edited by: AceFrehley03 ]

[pro-five-oh]

RJ, nope the sound is a constant, low volume whine. Sometimes I think I hear it get louder when I floor it, but it isn't ignition interference. I think it changes tone when the voltage regulator kicks back and forth, because the car will idle but the sound changes. I bet its that damn alternator.

The 130 amp alternator isn't a big step up, this one is basically the same 3G design. I thought it was a 130amp, but I think the computer at the parts store said it is a 120.

[RJ Sclafani]

I was originally going to say what Ace said, but I too figured you had checked everything. Well, try changing the alternator (since its waranteed) and re-check ALL grounds. I really don't know what to tell you other than that.

[pepsi2185]

Is it a whining, or a humming like "motor boating" . It may not be the alternator, by all means have it tested, but it could also be feedback through the amplifiers. Like on stage at a concert when the mic gets too close to the speakers, like an inductive or magnetic interference. A ground loop isolator is a nice bandaid it fixed one of my small systems oscillating problem. I was to lazy to find the real problem and that patched it for me.

Keep us posted on that alternator.

Big Joe