Transmission goes "bang-bang-bang" in reverse...

[blackmercedes]

Years ago I sold my 190E 2.3 to a friend of mine. He's kept the car since, and came to have lunch with me today.

As we were saying goodbye, he put his car in reverse, and it made this awful "bang-bang-bang" noise. He immediately put it in park and let it idle for a minute. Then he tried it again, and it did it again. He backed out of the drive so that a tow truck could get access, and it stopped. So he drove off.

Hhhmmm?

He just called, and said it hasn't done it again. We're both puzzled. If it makes any difference, the temp was about -26, and the car had sat out in the cold.

Any ideas?

Car has 590,000 kilometers (366K-miles) but the tranny is a new MB unit installed at 500K, so it only has 55K-miles on it.