I tapped my side pipe with a rubber hammer to find the part of the pipe
had the noise. Mine was bottom back. So I took it off the pipe and cut a
1 1/2 x 1 1/2 square out in that area and found a nice piece of old metal
slag. After removing that piece I mig welded my cutout back in. It's under the pipe so you don't see it. A litte thouch up with some high temp paint and good as new. I did try sheet metal skrews first thinking the inner pipe was loose but that didn't work.
Good Luck
Bruce
