Why does my MBP overheat when I'm not using it?

This has been an issue for several months now.

I've read many posts in help forums on different sites. So far I have done things like reset PRAM, did an SMC reset, re-installed the OS, opened and cleaned out any dust, replaced both fans, and last night I reapplied thermal paste using the ifixit guide :).

And it runs cooler--when I'm using it. (SMC Fan control clocks it at 95 degrees Fahrenheit). But when I close it up and go to bed, by morning, the fans are running full speed and its burning up, and the screen is completely dark. It sits on a wooden coffee table when not in use, and sometimes its fine, while other times it's not. I make sure it has enough room around it for proper ventilation, and at this point I'm planning on purchasing a cooling pad for it to sit on, but I don't just want to treat the symptoms!

Any ideas as to what is causing it to overheat when not in use?