I don't know of any clearance issues with the NI Dual. Mine fits perfectly of course its on a coupe. I don't know if that makes a difference. As far as loudness? They are I bit louder than normal I think but nothing crazy. It's more of a deep tone and I'd say nowhere near 112db. I also recently put silencers on just to get it as close to normal as i could. IMO it helps a little bit and even seems to change the powerband a bit but I can't say they were worth the $80 I paid.
So in conclusion

IMO, they aren't loud enough to need silencers and you shouldn't have any clearance issues.