JASMA isn't a brand, it stands for Japanese Automotive Sports Muffler Association. It's basically a group which approves exhaust components to a standard.
my raspy sound comes on around 4000, but only under full throttle. mufflers have been found to work, depends on which/brand/etc.
slipping clutch? revs would 'free rev' in that case though.
could also be electronic related, injectors, sparkies, coil packs, etc. trouble shoot it and eliminate it one by one.