exhaust question

[highspeed]

i have a pair of 2007 df200 after running 10-12 hours when i got back to the dock all the exhaust was comming out the props none out of the exhaust port on th back of the motors, this happend once before on the port enging when i checked it the next morning ti was working fine. no alarms, run great, any ideas what could cause this?

[boats.net]

Ports on back are exhaust relief, wont always have exhaust coming out.