After a normal day of driving and turning off the engine. I hear a popping sound, sorta like popcorn poping in the bottom of the car. The sound gradually goes away but was wondering if this is normal. Does anyone hear any noise once they shutoff the car or is it completely silent. You'll hear it if it's at night time when it's more quiet.

 

It's most likely the catalytic convertor. It occured on my 03 MCS and when sold at 45k miles, I didn't have any problems associated with the exhaust.

 

I've always heard this on all my cars.. I think it's your exhaust/catalytic metal since they are going back to their original shape after the heat has expanded them after driving..

///Gilbert