Have a 1999 Volvo S70. Heater blower motor runs fine, but makes some sort of noise (kinda sounds like a blockage or wind going through a tunnel), as the fan is increased towards maximum. Noise seems to be associated with rainy weather and will actually go away after a few days after the rain has stopped. No water leakage is noted around the blower motor assembly and I have actually changed the blower motor out and the noise is still there.

Any thoughts????