Results of next text:
Restarted the game and was already set up to play a practice match on grass - two points into the first game the ball sound stopped again.
Did not change any settings or anything - stopped the match and changed the surface back to clay and started a new practice match - played an entire set without any ball sound issues - definitely seems surface related somehow.
Don't get me wrong - love the game completely! Just want to get the ball sound working on other surfaces. Will try something other than grass next
FYI I am on a Pentium 4 PC running Windows XP with a SoundBlaster X-Fi soundcard.
Go Tennis Elbow! Thanks for looking in to this!