I was driving my 1986 300e on an especially hot day last week. I turned off the radio 'cause there was nothing good on and I heard a strange noise coming from under the hood. It wasn't especially loud or high pitched, it just sounded like a humm or a whirl. It changed as the engine accelerated. I pulled over and checked under the hood. I could swear it was coming from the alternator. The tempature is fine, the oil level is fine and the car seems to be charging. Later that day, after it had cooled down, I decided to drive it home (about 30 miles) It was late in the evening and the weather had cooled down quite a bit. The sound was gone (?) We took it for a quick spin last night and the sound was gone. Today it's kind of warm outside and I took it about 3 miles. The sound was there. It comes and it goes. I asked a friend who's kind of a back yard mechanic and he says the alternator berings might be getting tired or aren't getting properly lubricated on hot days. He admits he doesn't know Mercedes Benz's very well, so I thought I'd ask you guys. Sound familiar?