the room tone of my audio seems to be a bit noisy because of vents which couldnt be turned off. do final cut or avid have some sort noise gate control which will cut the hiss and leave the audio from the actors at a good level?
there are noise reduction filters in soundtrack pro or stand alone (soundsoap) they change the quality of the sound, but it may improve what you have (so will a music bed.
like saneproductions said, there is a nifty function in Soundtrack Pro for reducing or nearly eliminating a noise floor. Simply record the dry room noise for a few seconds, use it as "noise fingerprint" and remove it from the actual recording. The larger the fingerprint is, the more accurate are the results.
also, try grabbing room tone from an equivalent sized and reverb quality room...it might not be exactly the room that was shot but no-one will know the difference...it's done all the time...