ive done a lot of research on this.
on our engine, rasp is mostly coming from the combination of 60 degree with an xpipe design.
what ive found that other cars have done to eliminate the rasp is one of these..
thats a magnaflow tru x muffler. think x pipe in a muffler.
you could put one after your x pipe, or alternatively, you could have an xpipe built with one