1994 c280 75k miles.

Sometimes when I put my car in gear it will make a humming noise. It won't do this when in N or P, but will in all other gears. It's almost like a humming/buzzing sound. It goes away in a couple of minutes once the car is warmed up. It has me concerned though because I know it's not going to go away on it's own. Last transmission/converter change was 10k ago.

Does anybody have any ideas what this may be?

Thanks

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