In city, the HVAC system works as designed. At highway speeds, apparent wind noise and/or increased fan noise becomes evident. This noise can be decreased by switching the fan to lower speeds, increased by turning the fan to higher speeds, or eliminated by switching the fan off. Any suggestions?

JamesC

 

Sounds like the bearing is going bad in the blower motor. Best bet is to just replace it.

If you want a quick temporary fix though, you can drill a little hole in the back of the motor casing right on top of the bearing "nub", and put some grease in there. The damage to the bearings has already been done and is irrepairable, but you can mask it for a while by using this trick

 

Hey, Oneblinky,

You're probably correct--I mean the car is 18 years old or so. How would vehicle speed, however, contribute to the noise?

Thanks,

JamesC

 

The air pressure in the plenum pushes the motor one way or the other in its bushings, up against a (worn out) thrust bearing... I have a car whose blower motor makes a noise only when braking, same thing seems to be going on there