Our Whirlpool electric dryer, mfd in 1999, has been great until now. Here's the issue: it will run for a while, then stop. After it sits for maybe 5-10 min, it will run again. I'm guessing it's some sort of thermal switch that just needs to cool for a little while, but I really know nothing about dryers. I took apart the vent (exhaust), and it was clean. Any tips appreciated!