belive it could be timeing chain or cluch houesing also try since its only at 2500 rpms make sure chain and sprokets are tight to lose of a chain will cause a pinging sound and sprokets ALWAYS need checking loseing a sproket at 100mph and ur dead ALSO make sure to check cluch houseing cause it sounds more like that than timeing cause timing would do it more at rpms(or atleast do it at differnt rpms)