Hi, I've been using a bold 9900 for about 2 months now, and recently I noticed the trackpad would start squaking when scrolling up/down or sideways, sometimes when I press down on the button. Then I did this and have no problems until now:
I pressed down on the trackpad pretty hard, then moved in all directions for a dew seconds(while still holding down trackpad pretty hard). After I did this a couple times, there is no more sound from the trackpad! See if it works on your squeaky bold 9900.