Hi, I had a skimmer with the new PSK1000 pump, what I did to quiet the noise is to put a brick on top of the skimmer cup to keep vibration down. After a month (it was new), the motor broke in and became quiet. Another note: I bought last year a Tunze 6065 with the new titanium shaft, it made a loud noise, I emailed Tunze guy Roger and he stated it needed to break in and would take a couple of weeks or so. After 3 weeks, it is so dead quiet, I have to look to make sure it is on.
Another possibility is to take the pump apart and soak all parts in vinegar overnight. Also check to see if rotor is spinning very freely on the shaft, if not correct the problem or get a replacement part.
Check with warranty dept. and see if you can also get a fix/replacement there.