When I step on the gas and above 2500 rpm, the engine makes a sound like it has a whole in the exhaust pipe, when it is parked and I rev it up it won't do it, only when I am going, could I have a whole in the muffler or something???? Thanks...AARON

 

could be the insides of the cat came loose or if you had double walled pipe it delamintaed and is making the noise.