My fairly new AC110 HOB is screeching like a banshee. First I noticed that the flow rate was going down. Knowing that it was the normal time for maintenance and clean out, I removed the filter and cleaned everything. I then put it back together, filled it, and fired it up. It suddenly started the screeching sound. I thought that maybe some sand got into the propeller when I was cleaning it. I took it back apart and thoroughly cleaned the impeller and its housing. Filled it up and fired it up again. It appeared that everything was good and then suddenly it started screeching again. Any ideas? I've had HOBs for years and years and I've never had this problem before!