Strange exhaust pattern with empty cats

[reddituser]

A few months ago I replaced my muffler and pipes (flowmaster 40, which I think is too loud for me), and in doing so I knocked some or all of the substrate off from inside the bank 2 cat. I opened it up at the I-plate and out popped substrate about the size of a golf ball. I assume the other cat is similarly depleted. Almost immediately I got a code for inefficient cat (can't remember the number) on that side.

My exhaust sounds strange, and I can't remember if it did before the cat was effectively gutted. It's like a pinging noise, a pulse almost within the exhaust note that drives me bonkers. Only happens when I'm in the 2k area and accelerating. Cruising, heavy in the throttle I don't hear it so much. But when I'm accelerating it is always there, and it's very annoying.

My thinking is that the empty cat is creating turbulence in the bank 2 exhaust stream and that's what's making the noise. I keep trying to research "exhaust pulse" and such but am not getting much in the way of useful information. Does anyone know what I'm talking about, or has anyone else had a similar experience? Heard of it? If anyone can provide any information I would really appreciate it.

I am thinking of just replacing the cats, or building my own delete-pipe/welding in new sections of pipe where the cats are now (off road only, of course). I don't mind the smell of gas (actually really like it) so that's not really a concern.

[ToyHauler]

the cats do a significant amount of quieting on their own and they must have both been working if you didnt have a code before. you thought the flowmaster was too loud but knocking the cats out are going to make it louder, you should always do the same to both sides now you have one bank making more power than the other. if you dont like the noise i would put new cats back where the originals were and you wont have to worry about the code for cat eff

[reddituser]

Well I'd rather not gut the other one and have even less power! I guess I am planning on replacing them both, I just want to know if anyone can confirm the wavy/pulsing exhaust note.

[mwall]

I punched out the catalytic convertor on my wife's old VW convertible and experienced the same weird exhaust sound. I think that the sound waves bouncing around inside the empty convertor shell are causing this. After listening to the wife nag for a few weeks, I finally welded in a piece of straight exhaust pipe and problem solved.