I have a 1994 c class having this problem same as a recent post. Some tech wanted to just change the vacuum pump, but I think they will charge me for the new one at A$1200 plus labour, but won't put it in because the problem is a cheap vacuum leak and make 1000% profit! The leak I found is in the tubing which fits on to the gizmo next to the fuse box with a few coloured tubes attached to it. One on the top right hand (standing close to the fuse box) has come off the back of the jack attached into the gizmo's socket. Can I simply glue it back on? The tube is too hard to force into the jack's rear end. The buzzing comes on as soon as you turn the key to position 2(dial lights on) and start and move off, lasts for about 5 minutes and in cycles of 1sec buzz followed by 1sec no buzz. This noise comes on all the time, never miss once when the car is started. Rear passengers think car is about to blow up!!! Whats the best thing to do now? Next item, the rear headrest won't go down, maybe due to another vacuum leak? Next item, the aerial makes a clack, clack, clack sound when it reaches its extreme length and also when it reaches full retraction. Whats wrong with it?