So i've had a and long VERY expensive battle with my exhaust system lately. I have my own theories but maybe someone else will know whats going on.

Vehicle: 2005 GMC Sierra. i purchased the vehicle as such:

Shorty headers
CATS deleted
stock Y-pipe
short 3"(?) I-pipe
Y-pipe
Dual thrush chambered mufflers 2.5"(?)
Dual tail pipes 2.5"(?)

This sounded great, but a baffle was rattling inside the exhaust so i decided to change it up from after the stock y-pipe. please note i found the exhaust shop used 2.25" tail pipes at this time, although i don't know what they were before.

Shorty headers
CATS deleted
stock Y-pipe
short 3"(?) I-pipe
Single in-out 3" bullet muffler
Y-pipe
Dual 2.25" tail pipes

This sounded fine but was super loud and had a loud rasp (metal bat against a metal trashcan) sound at exactly 2500rpm and no where else under moderate acceleration (1/2 throttle). So i added another bullet muffler before the first one which got it quieter but still had rasp. Convinced it was the muffler i used or the y-pipe i changed it again.

Shorty headers
CATS deleted
x-pipe
Dual 2.5"
Dual bullet mufflers
Dual 2.25" tail pipes

Much to my surprise this sounded almost identical to what i had previously, but just a tad deeper and still had the annoying rasp as before. Convinced it was the bullet mufflers i changed slightly.

Shorty headers
CATS deleted
x-pipe
Dual 2.5"
Dual Spintech sportsman mufflers (6 spin traps per muffler)
Dual 2.25" tail pipes

At this time i had to laugh instead of cry. Again, it sounded just like before almost, and STILL had the same rasp. In desperation i threw in the towel and bought 2 Thrush chambered mufflers like i had in the beginning. But because of a different muffler setup i could not hook up the tail pipes.

Shorty headers
CATS deleted
x-pipe
Dual 2.5"
Dual Thrush cambered mufflers
No turndowns, just pointed straight out under the cab

Not only did it sound BEAUTIFUL, (Big block chevelle with flowmaster 40's almost) the rasp was gone! So i took it to the exhaust shop and had them hook up the tail pipes again since it was very loud and long story short tail pipes are needed for my truck.

Shorty headers
CATS deleted
x-pipe
Dual 2.5"
Dual Thrush cambered mufflers
Dual 2.25" tail pipes

This quieted it down an extreme amount (quietest one yet) and the signature sound is almost gone, sounds a lot like every other change i had made and you guessed it, the rasp is back yet again.

So here is my theory, the shorty header have never changed and neither have the deleted cats since i have owned it, and i have had rasp ever since it went to the exhaust shop the first time, so i cant point a finger at either the headers or deleted cats. Although i don't know what the original tail pipe diameter was, the ones on it now seem too small (2.25") and then you add in a typical exhaust shop bend on a 2.25" i can only imagine that shrinks it to a 2" in those areas or so.

My last ditch effort is to have them change out those small tail pipes for as big as they can run for me which hopefully i could get to a 2.75" since the bends in the tail pipe might shrink it to 2.5".

Thanks for any assistance!!!!

 

Actually deleted cats are known to cause rasp. If you have a long run of straight pipe in there, installing a resonator should break it up a bit and help kill the rasp. Others have posted using a flow master merge killing rasp as well.

 

Vehicle: 2005 GMC Sierra. i purchased the vehicle as such:

Shorty headers
CATS deleted
stock Y-pipe
short 3"(?) I-pipe
Y-pipe
Dual thrush chambered mufflers 2.5"(?)
Dual tail pipes 2.5"(?)

No rasp when i bought the truck

 

What type of tip, if any, was installed when the new 2.25 tailpipes were put on? Slash cut? Rolled tip? Just bolted? Welded?

I've found just a change in tip style can effect the sound of the exhaust.

 

Its an RST truck so it has these:

https://www.google.com/url?sa=i&rct=...41727072969004

 

Add cats and 3 inch pipe and like a spintech chamber muffler.