It's seems that some sand has gotten into my AC70. It makes a low grinding sound, it's not too loud but I fear for the impeller and shaft getting worn out. Cleaning out the sand and lubricating the parts shouldn't be too hard. But is there a more permanent solution to this problem? My fish like to play with sand and at times it gets pulled in. I've read about cutting up sponges to put over the intake valve. Not sure how that works or if I'm even doing it right. Anyone have experience with fixing this problem?