mid 90's 850glt.........oem radio....everything works perfectly except........ the am reception is great when the motor is not running...at night it pulls in distant stations with no problem.....as soon as motor is started...i am getting lots of what sounds like alternator whine....the whine is rpm related......the faster the rpm,the higher pitch the whine goes....many times totally drowning out what is otherwise a very listenable far away am station........i would think this may be a grounding issue...i recall way back when, there was always a capicator attached to the distributor to help prevent this kind of engine noise making itself known in the radio.....comments? suggestions? solution? i know this has to be a common problem with this and probably other model volvos....i've read of the complaint several times on this newsgroup but i have never read a solution.........thanks for all suggestions....
When I worked in avionics I chased a lot of noise. The good news is that 80% of the problems were antenna grounds; the bad news is that a couple of cases defied all my efforts. I recall a French Socata that had magneto noise so bad I could hear it when it was flying nearby! I never figured that one out.
The normal reason for interference with AM reception is indeed grounding. The most critical area is the coax ground where the antenna mounts. Remove the antenna and scour the area of the body down to shiny metal where the metal part of the mount contacts. 120 grit sandpaper works, but my favorite abrasive for that is Scotchbrite. Remount the antenna with dielectric grease, silicone grease or even petroleum jelly and see what you have. You may also have to finagle with the hood ground, even to the extent of fastening a wire between the hood side and the body side of one or both hinges - but if another car parked along side yours doesn't hear the whine from your engine the hood ground won't help anyway.
If you still have a lot of whine things get a lot tougher. The next step is to make sure the noise is coming in the antenna by unplugging the antenna from the radio and seeing if the whine goes away. If it does, you will have to do some detailed investigation of the shield ground on the antenna coax. It should not contact ground except where it was designed to - at the antenna mount unless there is a filter, amplifier or other device hidden along the way. If it does not, the problem is in the electrical system. (I suspect you are hearing ignition rather than alternator; ignition noise is very raspy while alternator whine is fairly smooth.)
For the electrical system, start with the easy stuff first again. Clean the battery connections and look at the alternator connections. That probably won't help but you'd hate to overlook it and have it be critical to getting the noise out. Next step: measure the AC voltage across the battery with a digital meter - it should be less than 0.1 VAC. If half a volt or more the alternator almost certainly has a bad diode.
Still noisy? (Whew!) You may be dealing with a ground loop. These nasty devils are the result of current going through a ground path that includes the ground path of the receiver. The common resistance couples the noise into the receiver. At that point you might just want to swear off listening to AM, but if you get to this point check back and we'll work through your options together.
Simplest way is to check that your alternator has a working capacitor attached to it's output terminal. Then check that the radio has one across it's power input terminal. The emphasis is on WORKING capacitors.
All the best, Peter.
700/900/90 Register Keeper, Volvo Owners Club (UK).
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