1989 GMC C3500 Alternator Whine in factory radio setup

[MasterMech]

Anybody else have a '88-'94 GM truck with a high pitched whine in the radio? Any sucess in silencing it? I know this is common in these trucks and was hoping someone else has seen/fixed this so I can kill it quickly.

 

[semipro]

I've had this problem with aftermarket sound systems before. It was fixed by inserting an "inductor" in the power line to the radio. The device looks like a small transformer.

 

[Highbeam]

I've heard thos devices called filters too.

I have had moderate success with adding extra ground straps. Grounding the alternator case to the engine block. Checking that the radio ground is very good. etc.

 

[rustynut]

resistor spark plugs ?
rn

 

[homebrewz]

You can get a toroidal core filter at Radio Shack. Its basically a magnet in the shape of a circle and you wrap the radio's power cord around it. Sometimes the radio cord can act as an antenna and pick up spurious signals from other sources. Its not that uncommon of a problem. Extra grounding would help too. You may have a broken ground strap somewhere on the block.

 

[MasterMech]

Ok. I'm going to subscribe to the grounding theory. As for resistor plugs? They were installed along with wires/cap/rotor recently and the whine was present before then. Thank you all for the replies.

 

[Dune]

You can buy a radio noise suppresor at a marine electrical shop and hook it up.

 

[Renaissance]

Ground loop whine usually occurs between two devices (head unit, amp, aux source) grounded at different points. Since your radio and amp are one unit, it's unlikely that this is your problem.

The whine is either coming through the power lead, or through the antenna. You can filter the power supply with an LC network (inductor + capacitor).

 

[fbelec]

make sure that your antenna ground is good