Some people playing Race Driver have sound problems. I found a post on a Dutch forum with a possible solution. The link is Dutch, so I've translated it below.
Most sound problems with DTM Race Driver occure at systems with a motherboard with onboard sound (mostly on the ECS K7S5A with SiS 712 audio).
The solution is: don't use the SiS drivers who are on the ECS site, but use the oficial Realtek AC'97 drivers.
This could be the solution for systems with AC'97 compliant chipsets. It's not 100% sure it works, but it's worth trying.