I too have discovered the same problem with my Bold.
As soon as I snap the battery door closed, the sounds is cut in half.
In my case. if you press on the area around the LED flash, the sounds
with be effected. If you let go, its nice and loud.
There is an indentaion in the battery cover itself allowing space for the flash
thingy, but it doesnt seem deep enough for when the cover is snapped in
place, the sound is effected.
I was gunna try to use my cordless dremel and try to slightly deep the indentaion
in the bace of the battey cover and see if I can make a tiny bit
Is this a common problem?