I have a similar problem to this in which the pipe doesn't have any play but the push pipe has a split in it. When I move this pipe I can heat a hiss which I guess must the noise when under hard acceleration.
As a temp fix/test, I put some duct tape around the split so when I moved the pipe, I no longer heard the hiss..
Took it for a test drive and the hiss has gone! Finally!
Hope this helps.