Recently I have noticed about 15-30 seconds.

MORE THAN LIKELY THIS IS A DENT IN YOUR MUFFLER OR CATALYTIC CONVERTER---WHEN IT BEGINS TO COOL, IT FLEXES

THE LONG WAIT, PROBABLY RULES OUT, A BACKFIRE

YOU MIGHT QUICKLY STICK YOUR HEAD NEAR THE MUFFLER AND VERIFY MY HYPOTHESIS, NEXT TIME YOU CUT IT OFF

IF YOU FIND THE DENT DOING IT, YOU MIGHT GIVE IT A WHACK ON THE CREASE (FROM THE DENT) WITH A HAMMER, JUST MAKE ANOTHER DENT (A MINOR ONE. BE GENTLE!) THIS "DISRUPTION" OF THE ORIGINAL DENT MIGHT STOP THE "POP"

KEEP US INFORMED

HOPE THIS HELPS

THE MEDIC