Exhaust noise on 98 SN

I have a question about the Exhaust on my recently purchased 98 SN. Have read quite a bit about mufflers and such here as I do have some minor seepage of water out of the fiberglass downpipes to the muffler.
I am getting a pretty annoying harmonic ? out of the exhaust around 2500 RPM's It disappears at just under 3000 and above. It is not any louder than above 3000 but more of a piercing acoustic sound that really bothers the ears. Really hard to explain it but you do not run at 2500 for very long.
I thought it might be the muffler leaking or vibrating but have looked at as best I can without removing the pipes. No water leakage from under the muffler and the rubber pads are in place on both sides and in the middle. Pipes and hoses do not seem to be rubbing anywhere.
Is this a normal harmonic to these hull hugger mufflers or do I have some loose baffles or ???