Hello, all (first post). I have been trying to figure out a certain noise that has developed within the past year or so of driving my 1990 limited. The best I can describe is a sort of quiet or subdued whining or humming, such as the sound of a faraway car horn through fog or something. This noise comes from under the hood somewhere, and I only hear it when my stereo is off (everything is quiet in the car). The noise is undetectable above, say, 30 mph or maybe 25, as road noise masks it. It is most noticeable when slowly cruising through neighborhoods, and it is definitely not a wheel-related issue. Sounds like an air leak somewhere or something similar. Lastly, when shifting into first, the noise immediately and simultaneously vanishes. I appreciate your advice!

If the tranny has a vacumn madulation valve on it, I would suspect that.

If the tranny has a vacumn madulation valve on it, I would suspect that.

Do you or anyone know how I can find this valve? I have a piece of junk haynes manual intended to cover 15 years of 3 models of cars, which tells nothing of any vacuum systems whatsoever (that I can find). Thinking seriously also of buying a service manual from somewhere. (anyone know of where?)

I believe that the valve is located on the front drivers side of the tranny. It is connected to the vacumn line. I'm not too familiar with the 3800 layout for '88 and on, but it probably is the same, if not similar to mine.

If you have a lot of miles on the tranny, it might be a gasket of some sort going bad inside the tranny. You would have to ask others here if they have had similar problems with that one to be sure. If that is the case, some Lucas Transmission Fix should solve the problem.

Google "Chassis Service Manuals" to find a manual specific to your car. They cost about $60-$100+.

Hello, all (first post). I have been trying to figure out a certain noise that has developed within the past year or so of driving my 1990 limited. The best I can describe is a sort of quiet or subdued whining or humming, such as the sound of a faraway car horn through fog or something. This noise comes from under the hood somewhere, and I only hear it when my stereo is off (everything is quiet in the car). The noise is undetectable above, say, 30 mph or maybe 25, as road noise masks it. It is most noticeable when slowly cruising through neighborhoods, and it is definitely not a wheel-related issue. Sounds like an air leak somewhere or something similar. Lastly, when shifting into first, the noise immediately and simultaneously vanishes. I appreciate your advice!
I believe this whine might be coming from your Alternator. I had this with my 2001 Silverado. The dealer disconnected the Alternator and it stopped, hooked it back up and it came back. Now I have this on my 2003 LaSaber. It is there up to about 25MPH. My wifes 2002 Century does not do this! The dealer said it was normal. Oh Yea, It doesn't do it all the time, might be when the battery is full charged or needs a heavy
charge.

Or it may be a wheel bearing...

Alternator is something I didn't think about. I remember driving my first car ('81 prelude) on wet days the alternator caused a whine in the stereo system, but not from under the hood. I'll try checking that out along with the wheel bearing. Waiting on a service manual to come so I can troubleshoot the vacuum lines.