W124 brake-pad light question

[McLoffs]

Hello everyone. The brake-pad light on my 1993 300E recently came on. I assumed this just meant it was time for new pads, but after poking around on here it sounds like the light is supposed to come on only when the brakes are being used. Is this correct? Well, I ask because the light on my car is coming on right after the car is started and the brake pedal isn't being touched, and comes on sometimes while driving (it'll come on and off while driving on the highway, for instance).

Any ideas what might be causing this?

Thanks,
Mike