T60 + Vista on battery = delayed sounds?

[shinjiplus]

i couldn't find anything like this on search but i remember reading a thread on this before.

in vista, when you hold backspace to repeatedly delete a line of characters, eventually it will reach the beginning of the edit box and start the "ding" sound.

with the AC adapter plugged in (in the mini dock) the sound will fire rapidly until i let go of the button and the final "ding" will sound completely.

when i'm using my T60 on battery, each "ding" is sounded almost completely. so that means i could potentially hear "ding" sounds after i release the backspace button and it is really annoying.

any ideas?