train noises from exhaust

i have a 2000 z28 and my problem is when i accelerate, around 2500 rpm my muffler sounds like a freight trains horn........is this normal.....my car is stock 4 now......advice needed!

its all the POWER trying to get out :) but seriously, sounds like you have a resonation, either some part of internal metal has come loose inside the mufler, and is vibrating, or a metal sheild on the exhaust system is making contact and vibrating at that particular resonance. aside from that, have no clue.