Welcome to AA!
Is this a hang on back (HOB
) power filter? If so, there are several possible problems:
Is there something stuck in the impeller?
Is the filter level?
Is the filter touching the wall behind the tank?
Is it just a bad design?
These are the four things I look for with my AquaClear filters. I don't know about the Tetra filters, but my ACs do make some noise, even when they're set up right. I blame it on bad cover design. The cover on the AC70 is a little flimsy and it rattles, but the filter is awesome.