Anyone use one of the aftermarket CATs from idparts?
My '06 has a GDE eco tune and cat delete with magnaflow muffler and is noisy AF.
Thinking about re-installing a CAT to make the noise levels acceptable again.

You’d probably be better off just getting a different muffler.
Adding the cat back in won’t make much of a difference.

Noise is subjective.
I have no cat and no muffler. Exhaust turns down right under the passenger seat.
Yes it’s loud but not unbearable. I like it and surprisingly my wife doesn’t complain.

Don't add the CAT back, they are expensive anyway and harm turbo performance and raise EGT's.
Just replace/upgrade your muffler and be sure and keep the tailpipe in service all the way out to the rear of the vehicle.

I have NO CAT, a Flowmaster 942542 Series 40 Delta Flow Muffler with tailpipe and chrome tip to get it out past the rear bumper.
I have no drone at any speed and very little exhaust noise, only a pleasant note when accelerating hard.

I'll have to check pipe diameter and look into flowmaster, haven't ran one for years.

The Flowmaster 942542 Series 40 Delta Flow Muffler is an exact replacement for the stock muffler.
2.50 Center In / 2.50 Offset Out

Just remember, a CAT diminishes Turbo performance some and also raises the exhaust gas temperature coming out of the engines combustion chamber due to the higher backpressure due to the restrictive nature of the CAT honeycomb. It's not there for noise control or to enhance performance. If your want better performance, fuel mileage, and lower EGT's, get rid of it unless you have to withstand a visual emissions inspection.

Elevated EGTs are not nec a bad thing. Sustained 1300* pre-turbo....different story.
While the CAT is not intended for noise control it does give that benefit. Better performance and MPG by removing the cat is debatable but quantifiable. A good example is in the Cruze Diesel, there are 2 cars I'm aware of that have hit 1,000 mile range on single tanks. One is fully deleted and the other is 100% stock. Where the deleted cars see their advantage is town driving with no regens.
The turbo design can have more effect on back pressure than a clean CAT. Another example was my 2000 6.5TD. The GM turbos have a very poor designed exhaust housing causing excessive drive pressures regardless if a CAT is installed. When I finally replaced the stock exhaust on my truck with a 4", including a 3" DP and mandrel bent x-over there was no measurable gain in MPG and I still had to drive by the EGT gauge as max sustained #s would be too high towing.
Now if someday I decide to do a full hot tune I could see where that may overwhelm a stock CAT but would a high flow aftermarket unit handle it?
FWIW, we don't have emissions testing but I still have the stock CAT and exhaust on my Dmax too. It gets rid of the haze and being a DD/tow rig I like it that way. Want smoke and haze? Have a couple 12V cummins in the yard for that, lol!

I beg to differ, any exhaust restriction that increases back pressure on the turbo increases EGT's.

I proved this on my Dodge 24v Cummins. (No CAT from Factory)
It has an EGT Autometer gauge and when I replaced the stock exhaust system with a 5 inch turbo back to rear bumper along with a straight through turbo muffler, it dropped the EGT's 150 degrees when pulling a load up long hills.
Air intake will also affect EGT somewhat. I played around with different air filters and the bigger and less restrictive filter would help keep me out of 1300+ when pouring the fuel to it.

But to each his own, if you want a CAT on your vehicle, it's yours....

You must of had a tuner on that 24V to hit those temps!
What year is it?

98 24V and yes it has lots of goodies...and rocks!

Had a 98 as well but was a 12V, QCSB Sport. Was broad sided 3 days after we bought it.
Also had a '89, 01 and now a '95.

Looks like you like those 12v's.