Problem with Eheim 2213

I recently pulled an Eheim 2213 out of storage (it was stored clean). Since hooking it up again (bio media only), it's been making this rattling noise. The air seems to be all out, so that's not the problem. Any ideas?

A little more detail... When I took the impellor out to make sure it was clean, I accidentally cracked the ceramic axle. I ordered a new one from BigAls and installed it, then started it up. This is when the rattling noise started. I took it apart again and looked very closely. You know those little rubber gaskets at either end of the axle? The old ones had a little notch in one end so the diameter of one side was smaller than the diameter of the other side.

The new axle came with rubber gaskets that did not have that notch at the end. I did notice the new gaskets sticking a lot in the holes.

Eheim's label on this part does say it's for the 2213. Maybe they changed the design, but the gaskets didn't work on my 2213.

I reassembled with the new axle and the old gaskets and it's running pretty quietly now, no more rattle, although it does have a hum that it didn't have when new.