I think once you have all of the tin work back on it, it will quiet up a bit. The air cleaner not being on too will make it sound different also.
I should tell you, unless you remove that muffler, you'll have a tough time getting the engine drive belt guard back on. I also don't think there is enough clearance to screw that muffler back on after the belt guard is installed without scratching the paint. The high ribs of those mufflers make it difficult to get the muffler lined up correctly.