It could also be the unknown resonator that was welded in that needs repacking.
For reference I have the resonated version of the perrin 2.5" but also a catless header, and hiflow catted mid-pipe. Other than on cold start I wouldn't call the setup loud or boomy. I guess we all have different tolerances and expectations of volume tho so YMMV. Volume wise I think my setup is on par with something like an HSV
