What could be causing this?
 

Last night I moved my 7 from the street to my driveway (in the process I took a few trips around the neighborhood to knock off the spiderwebs). When I parked it I left it running and opened the hood to see that only ONE of the RB header pipes was glowing almost red hot. I have never seen this before. I have seen BOTH pipes glowing, after some spirited driving, but not ONE from driving miss daisy to the corner store. Any thoughts?

Bag plugs making it run too rich in one rotor or sticking injector causing it to run too lean or rich in one rotor.