Why isn't my exhaust loud?
 

I just put on a cat-back exhaust with a thrush welded muffler single in dual out to 3.5 inch tips. The exhaust has a nice deep rumble to it. It rumbles louder at lower RPM's and fades out completely at higher RPM's. I wasn't satisfied with it and wanted it louder, so I cut the pipe right behind the cat a little bit, beat the pipe in, stuck a bar inside, and noticed the cat had already been gutted (bar went inside the cat and I didn't feel any guts). So I pryed out the bent pipe and welded where I cut it.

The exhaust is so quiet for the cat to be gutted. I've heard trucks around here absolutely roar annoyingly loud with just a single in dual out muffler.

Is it because there's no resistance to output flow, and this causes no resistance to roar, so to conclude is that it flows smooth? How do I add resistance to make it roar absolutely loud?

It's a 1993 k1500 5.7 liter engine.

Thrush mufflers aren't loud mufflers. If you want obnoxiously loud just cut the muffler and put a y-pipe in its place.

do you think a flowmaster 40 would be loud?

Loud, a lil more than the thrush. Annoying, very much so in trips