my powerbook trackpad button does that sound, too.
i bought it a year ago and that sound just appeared a few weeks ago. i just hear it when i push the button on the right side...
I have same noisy problem on the left side. Its really irritating. Bought mine from apple in Sep, just before they released the core duo 2 in the UK. So I have the core duo (1) and a noisy mouse. My life couldnt get worse