Stereo Hum

Gixxed · Sep 22, 2009

I have a 99 Mustang GT. The stereo is the stock Mach system and occasionally I get a Load Hum the goes low to high pitch with the RPM's of the motor. Sometimes I can turn the radio off then turn it back on and it will go away. It seems to happen when I corner a little hard as well. I cannot find any loose wires. I have check the alternator connections as well.

Anyone have and solve this issue?

Thanks
Eric G

35thstang99 · Sep 22, 2009

i have the same problem in my 99..its goes on for awhile then stops for a while i have narrowed the problem down the the amplifer be hind the deck it was happening the other day and so i pulled the radio checked all conncetions and then banged lightly on the amplifier and it stop and hasnt come on since..this weekend im going to pull the amp and see if there is a problem with it...if thats the problem ill let you know cuase im sure itll be ur cause of the hum too

GDawg · Sep 23, 2009

You have what is called "Alternator whine"... There are variations in voltage in the powerline or picked up by the antenna. You can eliminate it by installing a "radio choke" or a "filter capacitor". Contact Car Toys or your local high level car audio shop for this. You connect them into the power feed side of the radio.

Nightstick · Sep 23, 2009

A bad ground can cause this to happen. Check all your ground connections.

trinity_gt · Sep 23, 2009

Nightstick said:
A bad ground can cause this to happen. Check all your ground connections.

+1.

"Alternator whine" gets into most stereo systems -- aftermarket or otherwise -- because of poor ground return circuits or circuit layout. It's generally caused by power-ground currents -- all or part -- returning on signal ground conductors or by laying power and signal conductors adjacent to one another.

If a stock system has suddenly developed such a whine, I'd verify all system grounds. If there's no reason to suspect anything there, it might be worthwhile having the alternator checked for a bad diode in the rectifier bridge. Excessive ripple on the output of the alternator may overwhelm the line regulation and filtering ability of the head-unit and amps resulting in a whine in the speakers.

Gixxed · Sep 24, 2009

Thanks guys..... I have been having the alternator cause a code for the cam sensor occasionally. I have been told that this is a diode issue of some sort as well. Do you think this may cause the whine as well? I am going to check the grounds as well. But the stock system should not need a filter. It is just weird to be able to shut the radio off then turn it back on and have it stop. (most of the time)

GDawg · Sep 24, 2009

Gixxed said:
Thanks guys..... I have been having the alternator cause a code for the cam sensor occasionally. I have been told that this is a diode issue of some sort as well. Do you think this may cause the whine as well? I am going to check the grounds as well. But the stock system should not need a filter. It is just weird to be able to shut the radio off then turn it back on and have it stop. (most of the time)

Bad diodes in your alternator can cause all sorts of problems. Especially computer problems. Too much AC in the DC circuits.

Gixxed · Sep 25, 2009

Fantastic. I guess I have to break down and buy a new alternator

GDawg · Sep 26, 2009

Gixxed said:
Fantastic. I guess I have to break down and buy a new alternator

Do you know how to do an "AC ripple" test? That will tell you if your diodes are going out.

Gixxed · Sep 26, 2009

I do not. Is there a place I can go for instruction

GDawg · Sep 27, 2009

Gixxed said:
I do not. Is there a place I can go for instruction

Right here...

Do you have a volt/ohm meter?

BlownFiveLiter · Sep 27, 2009

The stereo ground is behind the kick panel on the driver's side, if you wanted to check that out as a potential issue.

Gixxed · Sep 29, 2009

GDawg said:
Right here...

Do you have a volt/ohm meter?

I do

Gixxed · Sep 29, 2009

StangGT1995 said:
The stereo ground is behind the kick panel on the driver's side, if you wanted to check that out as a potential issue.

I will check this as well. Thanks

GDawg · Oct 1, 2009

Gixxed said:
I do

Set the meter to VAC. Run the engine and put the positive test lead on the Alternator Battery Output (the largest connector on the Alternator) and the negative test lead on the Alternator housing for ground. You should have no more than .4 vac. If you have more, you have too large of an AC ripple. It will mess with your computers.

40oz · Oct 1, 2009

Gixxed said:
Fantastic. I guess I have to break down and buy a new alternator

a rebuilt alternator is just as good considering all they do is use the old pully and housing and re-wrap with new wire and circuits. Not that expensive either, and you can swap it in fifteen minutes tops with basic hand tools.

I wouldn't call it "breaking down," rather "getting off easy, "

Gixxed · Oct 2, 2009

Thanks I will check that A/C ripple test out this weekend while putting on new brakes and rotors.

I know rebuilt is just as good I just have the second one in less than a year and I am just a little tired of buying alternators. (BTW Remanned). Just a pain.

GDawg · Oct 2, 2009

Gixxed said:
Thanks I will check that A/C ripple test out this weekend while putting on new brakes and rotors.

I know rebuilt is just as good I just have the second one in less than a year and I am just a little tired of buying alternators. (BTW Remanned). Just a pain.

I got an OEM Motorcraft Alternator from the junk yard (out of a Lincoln Towncar) for less than $30 and it was in great condition!

Skud · Oct 3, 2009

I had alternator whine in my 2002 GT after I changed out the Mach 460 system with a Clarion head unit. It wasn't too loud so I lived with it for awhile. I only really heard it over 3,000 rpm.

After I did the "big 3" upgrade the whine was gone. The big 3 upgrade entails:

- Upgraded battery negative to chassis
- Upgraded engine ground to chassis
- Upgraded alternator positive to power box

I also upgraded the battery to power box connection..

Thanks!!
Riley

Gixxed · Apr 17, 2010

So I changed the alt. whine went away and so did my engine start die start issue that tripped the cam sensor. it was an ac ripple. Thank you for all your help. been going good for a few months now without any issues

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