I have a 1993 600SL with 58000 miles. It is a beast. There is a strange irregular tapping noise coming from the SRS area in front of the passenger seat (the place where most cars have a glove box) . There is no relation to speed, air conditioning, anything. Any ideas?
Gary Pearce

 

I had the same problem - It is the Y-11 vacuum block -It controls the A/C vents and other functions. The longer it goes, the louder the clicking sound gets.

They are occasionally on e-bay for about $125 US