the blower is quiet on 1 and 2 but has a very loud noise on 3 and 4
when its cold it happens as soon as i switch the motor to 3 or 4. when its warmer weather it does not make the noise every time or just not as long. when i go for a long trip it stops after an hour or so. my other blazer did the exact same thing. maybe i need a new blower?

 

just an added thing the old blazer i had if i hit the blower housing with my hand it would stop the noise . i tried that today and it did nothing.

 

perhaps the bushings in the motor are starting to fail, i would hate to have to cut up the blower housing to remove it..