Loud crack in new side pipes when cooling down?

[facultyofmusic]

While working on the car I heard what sounded like a loud crack noise from around the side pipes region. While I had the sound fresh in my head I knocked around the car with my screw driver and found that the sound matches that of knocking the side pipe with my screw driver. I'm scratching my head trying to figure out what that sound could be. Are the side-pipes known to make cracking noises when cooling down during the first few heat cycles?

I can also make an identical sound if I drop a small nut onto the side-pipes from about shoulder height, but I did not hear the other sounds you'd get from the nut bouncing around on the floor.

I'm fairly sure it's nothing major, but if anyone has experienced this it would give me great peace of mind.

EDIT:
I heard it twice with about 15mins between them.
It was a cold and quiet hour of the night, so maybe it wouldn't count as "loud" normally.

[Blitzboy54]

When the pipes are hot they expand, then begin to rapidly cool when the engine is turned off. The cracking noise you are hearing is pretty normal and the sound of the exhaust contracting. Mine does it most times I shut the engine off. I suppose if it was REALLY loud something could have cracked but I suspect it's fine.

[Nigel Allen]

When the pipes are hot they expand, then begin to rapidly cool when the engine is turned off. The cracking noise you are hearing is pretty normal and the sound of the exhaust contracting. Mine does it most times I shut the engine off. I suppose if it was REALLY loud something could have cracked but I suspect it's fine.

X2 (my pipes are stainless)

[facultyofmusic]

Thank you gents!

[Scott L]

My pipes "tic" for a few minutes after a good run, but nothing loud.

[GTBradley]

I had my roadster "finished" and legal to drive, so I drove it out to the racetrack just to visit and get my first hour and a half long drive in. While talking to people over the open engine bay, with the engine off but still hot, we heard what sounded like a firecracker. It was startling and concerning, but I never heard it again and never found anything wrong. I finally decided that it was just a new engine with tight parts getting to know each other better.

[J R Jones]

In (suburban) high school a rich classmate had connections to score a USAC 427 side oiler. As if that was not enough, we put roller cam and two four barrels on it.
After the engine consumed a 57 Ford with "exhibitions of speed" the engine went into a 31 Ford three window coupe. Post driver's license, we were out late street racing and (metro) Police attempted an intercept.
WWII P38 terminology was a "power evasion maneuver" tail lights disappeared in the ether. Radioing ahead was not effective but VFR and prior conviction was.
The last leg home was made without lights and garage seclusion was made without observation.
30 minutes later the Police showed-up asking "Where is your coupe?" Tom replies it is in the garage. Demanding an inspection the garage door swings up and releases a cloud of hot air. The 427 tattled on us. The heat soak was emitting boiling noises and the headers were snapping. "We were tuning it earlier tonight". The police did not buy that, and the holding cell got another overnight resident.
jim

[drewr]

In (suburban) high school a rich classmate had connections to score a USAC 427 side oiler. As if that was not enough, we put roller cam and two four barrels on it.
After the engine consumed a 57 Ford with "exhibitions of speed" the engine went into a 31 Ford three window coupe. Post driver's license, we were out late street racing and (metro) Police attempted an intercept.
WWII P38 terminology was a "power evasion maneuver" tail lights disappeared in the ether. Radioing ahead was not effective but VFR and prior conviction was.
The last leg home was made without lights and garage seclusion was made without observation.
30 minutes later the Police showed-up asking "Where is your coupe?" Tom replies it is in the garage. Demanding an inspection the garage door swings up and releases a cloud of hot air. The 427 tattled on us. The heat soak was emitting boiling noises and the headers were snapping. "We were tuning it earlier tonight". The police did not buy that, and the holding cell got another overnight resident.
jim

Bad boys. I'm amazed at all the stupid stuff I got away with in high school. Good story.

[tonywy]

My Harley makes those noises when shut off. I think it's the heat shields.