This morning listening to the radio the volume went down and a slight whine came back.  I can turn up the volume and not hear it but listening to people talk it's pretty obnoxious.  It seems to be coming from all of the speakers.  Also the whine seems to get faster according to the speed I'm driving.  Any ideas?  Also I noted last night that the back light for the radio display went out, so I can't see the time or the radio station numbers.  Do you think there may be any connections?  1990 Bose cassette player

|UPDATED|10/12/2012 8:05:52 AM (AZT)|/UPDATED|

Alternator has an issue.

My 85 did this 3 times while under warranty. They changed internal parts on the fdirst two occasions. The third time, I put an aftermarket regulator in it, and problem never came back. That was 25 years ago, alternator has never been off the car since.

Are we looking at other issues if the alternator isn't working to hot?  I replaced it this summer with a re-manufactured unit from the chevy dealership.  Am I working with 'dirty' electricity?  I don't want to burn out something important if my alternator is running to high or out of control.  thoughts? 

I'm familiar with alternator whine in sound systems. You have a 90. The 90 has a CS130 alternator. (Unless its a ZR-1). These are notoriously unreliable. I have the CS 130 in all of my other vehicles (4.3L S-series) that I've driven daily for 20 years for a combined mileage of over 600K miles. I have a ton of experience with the CS 130. The CS 130 fails electrically and mechanically, but I can't say I've ever heard alternator whine in the stereos. So it may be something else.

It's easy to prove / eliminate the alternator as the source of the whine:  With the engine operating, and the noise present, unplug the connector on the side of the alternator. This will disable the alternator, there will be zero output, the car will be running on battery power alone, which is very stable. If the whine is now gone, it was coming from the alternator. Plug it back in, and the whine should come back.

You can monitor voltage on the inst cluster. It should be 13.8-14.2 with a charged battery, on a shirt-sleeve day. (Temperature influences voltage). Turn on some loads: Headlights, rear defog, high blower. Voltage may drop a few tenths, but still be in the 13.2-13.8 range, especially with increased RPM. If voltage is in the low 12.s, and won't increase with increase in RPM, you have a bad alternator, (defective bridge rectifier or stator) and could well be the source of the whine.

Last thing for now: If the above tesets don't seem to indicate alternator problems, try "listening" to the whine on different sources on the radio. AM, FM, Cassette, C/D. If it's only present on AM, the antenna may have issues. If it's on all sources, it may be an internal problem in the stereo with power supply filtering.

There's some ideas to get you going. Good Luck.
DaveP

I agree--- I've had the same problem before with certain reman alternators and the internal regulators they used. I've also seen alternator "noise suppressors" (capacitor) for sale online at some "stereo" shops...can't say how well it would work in your case.

|UPDATED|10/14/2012 5:07:17 AM (AZT)|/UPDATED|