I'd like to disable the sound on my APC BK300C battery backup. I found
the little device on the printed circuit board which is causing the
really annoying and nasty sound. It's a black circular object. Is it
possible to fill in the hole thereby muffling the sound? Or can I
remove the object and re-solder something in it's place?

Here's the little noise maker itself:

http://www.opalfire.net/front.jpg

Here's the top of the printed circuit board ... the circle is where
it's located.

http://www.opalfire.net/top.jpg