Car suddenly sounds quieter??....
 

Hello, I have a G35 sedan and i have been running it with a resonator and muffler delete for the past year and about two days ago i noticed that car sounded a lot quieter than it normally is. I have had no recent maintenance done to the car whatsoever. The only thing to note is that i noticed my car was quieter after getting some gas. Could bad gas somehow cause the car to sound quieter? Friend suggested it could be my catalytic converters. Anyone else ever had this issue?

Yep, it's happened to me before, you probably got some bad gas with low octane.

Did the issue fix itself? I ran through the bad gas and currently have it running on 93 octane.

The only time it ever happened to me it was immediately fixed with the next tank of fuel.

I am about to run out of gas that i put in after this issue started happening and it still persists. I wasn't even sure if ECU reset would help but i did it anyways and didn't make a difference. If it were the catalytic converters i assume they would throw a code wouldn't they?

Not necessarily, the downstream sensors won't throw a code until the data they're sending is out of spec. You can have melted spots in the cats and still have a running engine, Is there any chance that you got a bunch of water up into the muffler or something? I've seen wierd things happen like people parking right next to a high pressure sprinkler in a park that actually worked water back up into a muffler although it wasn't really a "muffled" sound it just sounded like complete **** and was belching water out when he was on the throttle. Took a week to finally get it all evaporated though.

The thing is that im running a pipe straight back from the cats. No resonator or muffler is present. Car is usually parked on an incline and there is no sprinkler system nearby. Would adding dry gasoline help get rid of water you think?

I'd say at this point it would be a good idea to disassemble the exhaust and see if there's something wrong with it or the cats. The bends on the cats makes it hard to see the element itself but you can with an inspection mirror and flashlight.

So it looks like the issue resolved itself...took some time but car sounds normal now. Thanks for your help Cleric!

Yep, sounds like bad gas. Glad it's all fixed