exhaust sound

[opey450r]

i have a 07 pete 379 with 565. have 7 inch straight pipes and when it get to around 1500 rpm it has a weird sound up in till 1700. has anyone else had that problem. we have a 05 tractor with same motor with same pipes but it doesn’t have that sound. no exhaust leaks all brand new from y pipe out. hard to explain noise with words. when you back off throttle a little bit the sound goes away and sounds like it should