I have a 99 Suburban with a bad smell inside the cabin. The closest thing I can say it smells like is propane. When I turn on the A/C, the smell goes away. I'm thinking it must be something with the exhaust, but not sure. Any help would be appreciated.

Check for leackage at/near the heater core front & rear, I had the same oder, very strong and turned out to be coolant leak, minor but very strong smell.

R. Sanders

Could be a catalytic converter problem, they can smell like rotten eggs!

A freeon leak has a similar smell to propane, but is most present when the ac is on. A plugged catalytic converter smells almost like a skunk, (especially when parked and idling), and throws a hell of a steam cloud out when you go through a mud puddle - especially dangerous because they are known to get hot enough to catch the floorboards on fire.