The dryer in this story is the Maytag compact dryer model MDE2400AYW
Last weekend I was doing laundry and when I pulled the clothes out of the dryer, I smelled a strong burnt rubber / plastic smell. Worried about a potential short or possibly a fire, I unplugged the dryer and checked the vent and what I could access without a screwdriver but no obvious scorch marks or other problems, so left it for this weekend to dig into.
Based on some web searches I was expecting a problem with the drum belt or perhaps a short or problem with the heating element. Found the service manual
here today on another thread here thanks to AJ, and started tearing it down looking for smoke. Found a tiny smudge of black when I pulled the heating element, but nothing burned. Took it down piece by piece and it wasn't until I pulled the drum out that I found the culprit. In the space behind the drum was about 3-4 cups of lint, half of was charcoal and crumbled to the touch. So it looks like over the last 6 years I've had this dryer lint has gradually been sucked into this space behind the drum and below the heating element until there was enough that some got stuck by the heating element long enough to catch fire.
In a word, I'm lucky my laundry didn't catch fire also.
Needless to say, I'm going to be much more cautious of this dryer and dryers in general in the future. No leaving the dryer running at night or when I'm not home. This is a problem since this dryer is ridiculously slow to dry clothes ~1.5-2 hrs per load. Part of it is the long vent (dryer room was put in the middle of the condo for some bizarre reason), but I wonder if the design of this dryer isn't part of the problem also. Is it normal for there not to be any intake vent bringing air in over the heating element? The heating element is off to the left and above the drum, and the blower sucks air in the back of the dryer, but there is no intake to bring air in over the heating element. This makes any heating incidental by air that manages to leak in by the element, or by convection from the element to the drum. I expect there's a need to keep the air from directly going over the heating coils, but is it normal to have the heating element so isolated like this? This seems like a risky design since the heating element is so close to an area which accumulates lint with no way to clean short of complete disassembly.
I'm glad I now have a much better understanding of my dryer, but I'm looking forward to moving to a place where I can get a full sized dryer and ditch this Maytag. I learned my lesson - from now on it's Consumer Reports, and avoiding Maytag as much as possible.
Oh, and pics for the record. Given the design, it's only a matter of time before someone else shows up here with the same problem. Hopefully it's fairly minor like mine.