W210 Heater Whine

[shawnmcknight]

Hi,
My climate control has a high pitched cyclical whine but usually only when
the passenger side has air directed at the feet. When on defrost it's
normal, and on the driver side it doesn't whine if I select feet as well. I
originally though it was a blower motor but if there is only one blower
motor, and it's well behaved on defrost, what should I be looking at to
diagnose the high pitched whine?
Cheers :)

[marcos]

Just check all the vents a open as my W211 whines a bit if one of the vents is closed off. Also might be worth checking the intake isnt blocked and that the pollen filter is clean, this makes a hell of a difference to the performance of the blower.