I bought the Privia the day after Christmas to start learning on. Tonight while playing "America" the C above middle C started buzzing from what I thought was the right speaker. Actually I was almost sure it was the right speaker. Anyway being scared to death because I had seen this problem posted many times before on these forums I tightened the wing bolts on a lark and the problem got worse (I have the matching stand and pedal kit). I detached the DP and laid it on the bed. Something just told me to play it before I boxed it up and called Musician's Friend. No Buzz.
Perplexed, I tightened all the screws and bolts on the stand, took off and reinserted the score stand, and put it back on. No buzz. Now weather it was a loose screw, the score stand, or just the way the DP had settled in the stand and was making contact with it I don't know, but there was vibration from somewhere that was harmonically interacting with that note to cause a buzz. The next time someone has this problem I would tell them to do the same thing and see what happens.