high pitch whistle ( Heater fan ) ?

[mickbilly]

hI all,
C250 deisel turbo. '97
high pitch faint whistle when engine running. was driving me mad untill I discovered it came from the air delivery vent near side door. the fan wasnt running. the noise stops when I turn blower control to first mark on dial.
not the number 1, the dot before 1.
could it be the voltage control unit on top of the blower motor?
appreciate any help I can get. thanks.
mick billy.

 

[television]

Sounds to me as though one of the vacuam controlled vents is play up, or something stuck in a vent like a leaf or piece of paper. try it for a few min's at max speed and see what happens

Malcolm