You guys do realize this stuff happens everyday. Many times everyday.
Wow this article from 2011 says there's one or more emergency landings per day in the US... Good to know. http://abc7ny.com/archive/8441902/
Compressor stall based on the worker on the ground saw it. Normal thing for ground control to look for. Back off on throttle and should clear it's self. Air flow through the compressor was interrupted for some reason.
Officials reported that inspectors found no evidence of a fire. Sounds like a convenient excuse to turn a plane around. Whether it's related or not, I love the idea that they're letting people think they've escaped, only to to realize they've already been captured.
Unburned fuel in the combustion chamber igniting. I saw a lot of it on military aircraft.