Loud knocking on frame! Why?

[scm320]

When I try to launch off the line or when I'm at about 80mph WOT I here and feel a loud knock on the frame and I think it might be the exaust but im not sure. Any thoughts?

[BrianH]

could be your exhaust smacking your rear diff.

[rr1911]

could be your exhaust smacking your rear diff.

+ 1

[bkotzman00]

try some new exhaust hangers and go from there

[Trainrex]

It could be your exhaust smacking, your rear diff smacking due to a weak mount, or a bad rear diff.

[$lick Rick]

do you have a rear diff protector and aftermarket exhaust?

if you do, it's a common problem
some grinding of the diff protector or removal of it would probably solve your problem