1. Try grounding the amp & turntable at the power receptical.
2. Check and see if the turntable motor is grounded.
3. Your receiver's phono-stage may be a bit dodgy...
4. Check that there are no fluorecsent lights nearby that is switched on while you are listening...
5. Pro-Ject machines are known for their humming & buzzing...

Best regards,
Dewald Visser