hey guys;
once i had the same problem and gmat pointed me to the all famous impeller glue mod. worked like a charm, there is no eheim that leaves my hands without the mod now.
easy way to check if it will work:
run the pump without tubing or rads in the kitchen sink, if quiet...
the link by grunjefjaert will do it.
also, more here:
http://forums.procooling.com/vbb/sho...&threadid=3777