If you have an amp meter you should check the amp draw vs the nameplate on the motor. Most squirrel cage blowers are designed to operate in a box with restriction. Your amp draw could go sky high without the restriction.

If the amp draw is too high put a piece of sheet metal partially across both openings to dial in the "Full Load Amps". ie. if it is rated for 3.5 FLA then set to 3 FLA. just my $.015

Oh, and rigging up a couple of filter tracks would also be a good idea.