Mine did this after I added sand to my tank and it would get stuck in the impeller.
It was sometimes horribly loud and annoying. I'm wondering if you just got it maybe just clean out the impeller/housing a little then try and run it? Maybe check to see if the impeller was damaged at all? Even small bits of debris could scratch up the body of the impeller.
I also noticed that sometimes when plugging in the unit that if I gently nudged the impeller with something while it made noise that it would sometimes correct its spin and reduce the horrible sounds. When this worked I wouldn't have to do it again unless the AC
had been turned off. I've even knocked on the outside of the motor with my hand and fixed the sound before.