4k rev

[Galant-UNIT(sur_texas)]

when i rev and get to 4k the sound of the exhaust goes out it fades out.
why? what can i do to get rid of the 4k limit?

[peanotation]

in the good 'ol days when i had the OEM muffler off my car and it was just an open ended exhaust, after about 4.5K rpms the exhaust would almost completely cut out. it was silent [the exhaust] but the engine was still screaming. with my old OTTO performance muffler and my current OBX B1 muffler, they both kept their tone nice and deep below 4.5K rpms, but after 4.5K they would change from deep and smooth to high pitched and screamy, but not ricey shit sounding. truly love my exhaust, i'll have to take some sound clips of it when i get the car back.