94 Z28 making odd sound from under car

I have a 94 Z28, when it was taken in to get the water pump fixed the mechanic found out that the right WYE pipe had a crack in it and welded it back shut. A few months after that I started noticing that after you go over about 60 it starts to make a weird grinding noise from under the right side of the car when you hit the gas from any point on. When you turn off the car you don't hear it anymore until you go over 60 again. Could this be the pipe trying to crack itself open again? Or has anyone else experienced the same sound but had a different problem?

I'd say it's a heat shield

Have you checked to see if the crack has already opened up again?
Im shure the weld rubbing against itself would make an odd sound...so that could be it, but Id check the heat shields first.