I may try this with my 79. I just got some int. insulation stuff this surely cant hurt. I bought a 82 firebird brand new and every once in awhile there was loud buzzing noise that would occur. Under warranty I even had the dealer look the car over a couple of times with no luck. Turns it was this type of heat shield on top of the muffler that under the right condition would vibrate like crazy and made the sound.
