First my check engine light came on last week,,while the car was idleing in my drive way,,I would guess the first thing to go would be an o2 sensor..oh sorry 96 850 wagon 5 speed,,car is a caddy so far...now then, a while back, I noticed upon start up that after 15-20 seconds or so the exhaust would get louder by maybe 10 decibels is that part of some exhaust restriction for like a choke?...I havent read about checking the codes yet as nothing has gone wrong with the car....Rog

 

Take it to AutoZone or Advance and have the codes read. Maybe an exhaust leak but usually the leak will get quieter as the parts heat up and expand.

 

No you have to be outside the car to hear this..I doubt anyone would hear it from inside...but it definatly opens up and gets louder...and it happens within 20-30 seconds of starting from cold,,infact the colder it is the longer it takes to happen...Rog