Grinding from my Eheim 2213

[Obsidius]

Hey guys,

I am running a 30 gallon FW system and my Eheim 2213 is acting up!
It randomly grinds in on itself, aaand that's spooking me. I've recently cleaned it out and even more recently checked the impeller for jams, but nothing of the sort to be found Anyone have any ideas as to what may be causing the problem?

 

[mott]

Probably air trapped in the impeller, give it a good shake!

 

[toddnbecka]

Pull out the impeller and look down through the center to see of it's out-of-round or simply worn much larger than the shaft.