My chubby 250lbs friend thought he would take my bike for a ride. When he sat on the seat, the bike made a popping noise. It wasn't too loud, but loud enough to make him get off the bike.

The bike is a brand new Cannondale Quick 5

I am trying to figure out what the pop was. I looked over the frame and no cracks are visible. All the spokes and wheels seem okay.

He says it felt like the seat went down a little, so it may have just been the seat giving in under his weight. But, there was no noticeable hight difference in the seat.

He was not pedaling or anything. He just sat in the seat when the popping noise uncured.

I am thinking it was either the seat, like he says, or the frame cracked or the spokes stretched or something.

Any advice or thoughts would be helpful.