<FONT face="Comic Sans MS">Matt,
Compared to my 1970 Trans Am with an M-21 4 speed, the Viper tranny is almost silent. Sure it does have some mechanical noise, but nothing unpleasant and in my opinion much quieter than I remember the old Mopar cast iron 4 speed.
The neutral gear rattle is normal and from what I hear the best bet is to just get use to it. Changing fluid type might help, but in cold weather shifting is more difficult. A dampened clutch plate might help, but since you're out of the factory warranty it'll be expensive and I don't think it eliminates it anyway. I just think of it as part of the car's personality.
I would suggest however, finding your local chapter of the VCA, joining quick and comparing your tranny sound with another Viper. With only a 90 warranty from the dealer you'd better be sure the trans is healthy, quick! Otherwise you could be spending $3500~$4,000 big ones...</FONT f>