Bigdawg is right. Talk to Bruce. He does carry both Eheim and Hydor and he knows his WC stuff really well.
Here's something he once emailed me:
"Hydor L30 is a powerfull pump in a small body, and yes it doesn't tolerate much air in the line, and that's perfectly normal. The impeller in the L30 spins really fast to give the intended 320GPH high flow, so if there's lot of air trapped in the lines, then the impeller makes a sound. Now this's not an issue related to Hydors only... Some German sites showed how to fix the impeller of Eheim 1048 and Eheim 1250 in the past. The reason for this is, all these pumps have an implemented feature called anti-clog. This feature allows the impeller to rotate 3/4ths of a turn, free from the shaft allowing debris to flow through the pump without getting clogged."
Just a little more info....
