Yamaha GP1200 sounds like a rev limiter

[dolphinsfan1966]

It's a 97 760 with a 1200 engine put in it. It runs out good, starts great, idles great and accelerates great as well. The gauge is sun damaged so you can't tell what speed or rpm you are going. But, when you get up to speed full throttle it almost sounds like a rev limiter or maybe cavitation is occurring, I can't really tell the difference between the two. But if I let off of the throttle a little bit it sound slows then goes away as I let just a little bit of throttle out. How do I tell if it is cavitating at top speed?