3.3TT strange noise when rpm is dropping

[chxei]

Hello people, I'm getting a strange noise when I let off the gas and the rpm is going down. It's like some actor making a thinking noise "hhhmmmmmm" or like hybrid car driving noises. It is mostly noticeable when the engine is at 2-3k rpm and I'm in sport mode, slowing down. Above 3k it's either not present or I can't hear because the engine/exhaust noise is louder. When in comfort mode it's audible when I'm in real quiet place. But when I'm in sports mode it drives me crazy, have to turn on music to calm down lol. Everything works normally, the car has all the power and has no CEL or smth. I live in kinda third-world country and dealer is kinda crappy, they always say we don't have time now, try next week. Don't know what to do.
Tried to get some data from OBD, only two noticeable readings I got were B1637 code and 'catalyst damaging misfires on cylinder 2' values ranging from -129 to 128, while other cylinders are dead zero. I think they are irrelevant to my issue.
I looking to hear your opinions, what can I do to investigate?

edit: I don't have this car for a long time so I don't know If I bought this way or developed in my hands

 

[Snicklefritz]

"Catalyst" instantly made me remember a 12 passenger Dodge van that we bought well used many years ago. The catalytic converter was all busted up inside and pieces jammed in the pipe hole. The power was way down too, go figure. The telling thing that might apply to your issue is that as the engine struggled to work around the blockage, it "hummed" very noticeably. It was like the car equivalent of asthma. Ha hah. After that expensive repair it was like a brand new van power-wise. you should check under there to see if there are dents in your CC. If so, then Ima guessing a piece is busted off enough to make a mild "hum" sound but not enough for you to have noticed any power loss, since this car has so much power to begin with. Report back.

 

[chxei]

"Catalyst" instantly made me remember a 12 passenger Dodge van that we bought well used many years ago. The catalytic converter was all busted up inside and pieces jammed in the pipe hole. The power was way down too, go figure. The telling thing that might apply to your issue is that as the engine struggled to work around the blockage, it "hummed" very noticeably. It was like the car equivalent of asthma. Ha hah. After that expensive repair it was like a brand new van power-wise. you should check under there to see if there are dents in your CC. If so, then Ima guessing a piece is busted off enough to make a mild "hum" sound but not enough for you to have noticed any power loss, since this car has so much power to begin with. Report back.

visual inspection of CC from outside looks normal, can't see anything wrong, but who knows how does it look like from inside? car has relatively low milage, 85k km, it has passed inspection about month ago and emissions was as low as it gets. If CC was busted I think on emissions test it would show up. Also I think that reading I get from OBD is pointing to the spark plug/ignition coil issue.

 

[Plakchup]

Yup, I would pull the spark plugs and check the ignition coils next! The primary cats are a pain to remove and the chances of breaking the studs is not a fun one.