(I am running a mac system with OS X 10.5.8).
I did a bit more playing and I found that if I use the mouse click + shift button to draw I hear the beeps for as long as i draw (like a filled circle).
This is typically how I draw ROIs.
However, if I use the side buttons on the mouse (which for me is a bit more difficult) I do not hear the noises.
xset b off didn't work for me either.
The beeps come through my main speakers which is why they are particularly annoying...
Thanks
Chad