Proper operation, if the same as my '92 300SE is the fans run occasionally when commanded by the A/C system to compensate for a rise in pressure in the condensor. Also will come on around 100C on the gauge in response to high engine temperatures. I'm pretty sure there are 3 stages - low, med, high.

My guess as to why they're coming on randomly, especially with a cold engine is a faulty temp sender for the fans. You can isolate the cause as being the A/C by leaving it off and seeing if the problem persists. If it does, disconnect the wire from the temp sender for the fans (don't know where it is on your car, but I think mine is on the thermostat housing) and see if the problem persists.

Hope this helps.