I have nitoced this too, although it seem to be more a problem on the remote end as it doesn't happen all the time. When someone calls me and their line is very quiet I just switch to speaker and flip the phone over. (So that the speaker is against my ear.)
I came acrossed this tweak today. I remember reading your above topic a few weeks ago and thought the following may or may not help you.
In-call volume change without sound :
You can change the following values:
within each of these keys the default 'Script' value is 'p' for 'play'
Change the 'Script' value to blank (erase the 'p')
No more annoying beeps and the volume changes quicker!
Edited by kevinbaby, 26 August 2008 - 04:13 PM.