I find this odd. I have an HKS Hi-Power with a MilSpec cat. Car is fairly loud after putting the cat on. But now I've noticed that below 40 degrees F it started getting quieter, and below 30 degrees F it is almost silent. I'm thinking it's because the air is more dense and the car is running leaner. Car is running a Cobb Stage 2 OTS Map. Does this sound like the cause for it (not that I'm complaining cause I like it quieter)?

 

Cold air will not make your car run leaner, the MAF compensates for air temp.

 

Then I find it more odd that it is so much quieter.

 

in the cold it actually supposedly be lauder, and as a temp rises the car gets quieter.
You can actually measure that.
At lime rock there is a limit for exhoust s noise. I couldn't pass it in 7 am , but i just dropped under it 10 am. They actually measure your exhaust noise at the spec.

 

That's what's confusing me. It's like someone swapped my mufflers it's so different.

 

Yeah, my Cobb Catback gets louder in cold mornings and I don't like it lol.

 

I won't say I notice any difference between ambient temps, but with a mil-spec cat and buschur bullit catback my car definitely seems louder after driving for 4-5 hours.... not that it isn't loud in the first place, but this shouldn't be due to fatigue since I wear earplugs on any drive longer than ~30min (more for wind noise than anything)

 

I notice a big difference, its been below zero here some days and the stock exhaust on startup is brutally loud, I try to get out of my neighborhood as soon as possible to not wake my neighbors.

 

my cold starts are ridiculous in the cold and i turn more heads on the road. i definately think it's louder in the cold.

 

I have a tanabe really loud too..

 

This may not be the case but my old viper did this. I also started to lose power. Then one day the car was warming up and started to stall and sputter. This was followed by a big bang. I happened to be standing behind the car and pieces of my cat came shooting out my tail pipe. The material had melted and clogged. Then exploded out the back. After that my noise and power came right back. May be something to consider if it gets worse. Or it could just be your imagination. Or your going deaf lol.