are you using a desktop mic or a headset? if you're going to use a desktop mic it's going to be trouble no matter what. if you use a headset and it's still an issue then look in your mic properties for mic boost and turn it off.
Join a league and use whatever voice chat program they use. rF/rF2 does not have inbuilt voice chat. http://isiforums.net/f/showthread.php/2172-Will-there-be-ingame-voice-chat?highlight=voice+chat Forum search works though.
Donnie: No, plenty of external apps do this as well as anything which could be programmed internally, and give more options.
yeah, I don't think they need to add in game voip... it's bandwidth they don't want to spare and clans and leagues already have Teamspeak and Ventrilo among others. if you want voip with your racing then join a clan or league. you're welcome to come by ours if you like, but my boys are a little rough around the edges and we're modding right now, not a lot of racing until we have a working mod for rF2. http://www.bringingthepains.com/