I have a 2003 Trailblazer where the fan just started humming with a low pitch and it definitely adds volume to the system when it's on - same noise whether it's on heat, a/c, or just the vent fan. It was working and then suddenly the hum started - yet the fan is still blowing air just fine. It is obviously coming from the blower motor - wasn't sure if this was a sign of it getting ready to quit on me or if it was something else anyone was knowledgeable about. Any ideas on how to fix it?

 

Sounds like it might be out of balance, or a bearing is going on it. If its out of balance, there might be leaves or some other junk in it, or a weight has come off of the blades. If the bearing is bad, you would CAN get it fixed, but its usually cheaper to buy a new motor