Always quiet as a church mouse.Now all of the sudden you turn it on and it rumbles loud and shakes the whole car.Do they go bad just like that?Thanks.

Maybe something is in the blower wheel. I found a dead mouse in a customers blower wheel once.

Sounds like you need to pull it to find the problem

theres another post in reference to this problem i think it means something is in your blower fan making it off balanced.

I had the same thing happen to mine several weeks ago. I pulled out the Cabin Air Filter from the cowl area under the hood and found some loose foam. From what I could tell, it was from the recirculation door seal. I tucked what I could back in place and pulled the rest out. Also found that the filter was the wrong one and put the correct one in. Haven't had any problems since.