From new my pump always made a little squeal at very low speed, when it first started up. Usually just two squeaks and it's fine. Now I'm noticing it seems to be louder (maybe my imagination) and longer - though still gets quiet at full speed. Today I was playing with it and found that at a low speed setting it will squeal continuously.
If this isn't OK, what could it be indicating? I'm sure I'm still under warranty - so I'm inclined to ignore it until it dies or it gets closer to the end of the warranty... still.