'06 MCS 81k miles. Lights came on while my wife was driving, car went into limp mode. I called AAA and when I got there, the car started OK (SES light on, and battery light, but no EML). I drove the car around and when I got the rpms up, the EML light came back on and the car went into limp mode. There was also a knocking sound coming from the top end of the engine which you can hear in the video (a distinct "tap tap tap"). After a 40 minute ride on the flatbed, the car ran fine at the dealership (SES light, no others) and I couldn't get the car back into limp mode. Also, It seems the knocking went away.

Anyone have any ideas what the stealership is going to tell me?