i can get a deal on a big gun exhaust system but im concerned about the noise, how much louder is it than stock?

 

You'll notice the difference by about 10 decibals. While a 400Ex stock exhaust system comes around 92db the pipe pumps it up to 102db. If necassary get a quite core silencer. Though not as obnoxious as many other leading brands the biggun will certaintly give it an added growl.