I have a dynomax Ultraflo muffler in exchange of the stock, all the pipe is still stock, but I just have it dumped by the rear axle so you can't see the pipe (street sweeper). they call it this cause when you floor it, it blows dirt up... Anyways what I wanna know is when I hit high RPM and then let of the gas the muffler Girgles and googles... Is this sound do to back pressure. Also I still have the cats on cause I can't afford O2 Simulators right now, do the cats creat alot of back pressure. Does any one have 02 simulators for sell and how good do they really work...

Silverado SCSB stepside 5.3
Dynomax Ultra Flo.

 

I have a 99 Gmc with the 5.3. I have no mufflers, and it girgles also. In the exhaust system you have a few different waves going down the exhaust pipes. what you are hearing is actually more of like a back suction. What is happening is exhaust waves are colliding with one another, but it isn't hurting anything one bit. The cats. Leave them alone. They produce minimal back pressure, and your engine does need some back pressure or you will loose horsepower.