Exhaust Noise

I am trying to figure out whether this exhaust noise is normal. Whenever I first start the car and take off, in between shifts (m6) the car makes what I call exhaust farts for lack of terminolgy. :) A "put put" sound. Maybe its what the board refers to as "Rasp". Anyway, it goes away almost immediately as I continue to drive and the car starts to warm up. It only happens if I take a while to shift between gears.

When I bought the car, the stock muffler was cut out and I believe a flowmaster was welded in its place. There is no marking on the muffler just numbers so I do not know who makes it. Judging from pictures, it looks like a flowmaster.

Anyway, I plan to replace the whole thing but I was just curious as to why it makes this noise and once I replace it with a better exhaust system, that it will go away.

Thank you for your time.

on start up...the cars run rich...

when you let off the gas, you are hearing a little bit of backfire i would say. it is more noticable with a louder (less restrictive) muffler.

it gets worse if you run a cutout.

i think it is basically unburnt gas igniting in the exhaust pipes.

I know on my car when I let off the throttle and coast for a little bit then slowly roll back on the throttle I hear a rumble even after the car is warmed up. I notice it even more with the cutouts open. Usually it only does it when the rpm's are at or above 2k.

I've had over a dozen LS1s.
They all do exactly what you described.
Its like a backfire. Don't worry about.

My car backfires like crazy when its cold... it vanishes after about 2 minutes though.