noisy powerhead

so i ordered 2 koralia evolution 750gph powerheads...and they arrived yesterday, so i installed them

well, one of them makes a loud freaking hum noise, while the other one runs completely silent.

can this be fixed? should i take it apart and play around with it or something? or am i screwed and do i need to send it back?

 

id take it apart then put it all back together, it could be as simple as a part not sitting right or an air pocket between the suctioncups or the pump resting on a rock. so take it all apart then put it right back together and if its still noisy then you can send it back. most prabably it is some air trapped somewhere or the pump touching something. have a fiddle and see how it goes

 

that was actually a lot easier than i anticipated. turns out the prop wasnt fully seated on the shaft.

all is well now, thanks!