I am not sure if you are into WW1 or WW2 birds? but loud is the problem without spending lots of money

If you like the WW1 planes the coolest setup I have seen is the guys that mounted a Paintball system on a 1/3 Pup.. They don't have it set up to fire paint balls but as it fires, and pops air out it does sound pretty good. I think there is a thread here on rcu somewhere.

I believe there is a video on youtube as well.