Sounds like you've got a clearance issue - if you'll pardon the pun....
At revs the drivetrain may be torqued enough to have a portion of the exhaust system touching either the floor of the car, the axle, the sway bar etc....I'd check that and maybe which way the clamps are pointing...you might just need to loosen and turn a clamp away from potential contact.
My .02 CDN
2014 GT Track Pack/Brembo/Recaro/Whiteline suspension system/Blowfish Racing shifter bracket - the 3.73 Torsen is so loud now that, with all due respect to Wade Chamberlain, BadFast has been renamed "The Whining Mistress"
04 1200 XLC