I own a 1991 420SEL. This is my first time on this forum and the third MB that I own (previous MB's: 1967 250SE and a 1984 300SD). Anyhow, my "new" 420 SEL has an annoying little buzzing sound coming from the fresh air intake duct for the Automatic Air Conditioner Cpntrol. This is the little grill on the overhead console (where the front dome/reading lamp is located). Thenoise is louder when the car is cold and the volume drops when the car's interior is warm. If I put my thumb over the intake grill, the noise goes away (or it is muffled). BTW, I had a similar problem with a noise computer fan. I suspect the problem is with the intake fan that pulls interior air into the A/C controls. Has anyone else had this problem? Is this a DIY project? I could just turn the radio up and then I wouldn't hear the noise. But this "little" problem, in an otherwise near flawless car is driving me nuts! thanks for your help!