What type of Mic are you using? If you have an omni-directional Mic, a "Dynamic" Mic, it will have more of a tendency to pic up other sounds around you,-(side, behind); an example would be your PSR 2000's 'internal speakers' sound. A Condenser Mic such as a Cardioid or Super Cardioid Mic will have less of a tendency to pick up other sounds around you plus they can achieve a higher gain before feedback occurs.

Make sure the Mic Stand with the "Mic" attached to it is not placed too close the PSR's internal speakers. Other things to check is the 'Gain' knob on the back of the PSR 2000. The general rule with me is to never set it beyond roughly 2/3rd's of Max volume. Another thing to check is the Mic Volume on the bottom of the PSR 2000's LCD display. I set that Mic volume to usually no more than Vol: 90. Another recommendation is when you use your Mic with the Mic Stand make sure the Mic is evenly spaced between both of the PSR's internal speakers and again not right on top of the speakers. Keep the Mic a couple of feet away 'back' behind the Keyboard where your piano bench should be.

Best regards,
Mike