check out "pinguin 150 with biowheel" i just got two two weeks ago, same things happening to me. went to lfs today and he gave me (looks like copper scratch pad type consstruction, but made of black plastic) tube covers, about four inches long, round with hole in middle. he said it was prob. sand
but now im wondering. please keep me updated. i put the covers on today and everythings ok so far. let me know if you're taking yours back. ty