I have a 1991 300se (W126). Recently the ventilation system has been making an odd noise. About one to two minutes after the A/C has been turned on, a noise that sounds like a large book being closed seems to emanate from deep within the center part of the dash board. According to my wife, the heater also is not working properly (now that she is back in South Carolina I have not worked up the motivation to verify this in 95 degree heat!).

Any idea might cause the noise? Would it be related to a poorly functioning heater?

Sincerely, Eric Powers