99 E 320 Brakes

Something is either loose or not round or both. Warped rotors is in my opinion the most frequent cause of this.

I tried the ATE "power disk" slotted rotors and swear by them now, not onlyhave they lasted longer and not spalted badly in the snoe like all my Balo's did but they do seem to collect the dust in the grooves like they're supposed to. They not expensive.

Barring any loose metal parts in your suspension I'd say it's new rotor time.

He said that power washing helped his issue. Seems more likely that it's something hanging like caliper sliding hardware is sticking due to dust causing the vibration.

Disassembling the caliper sliders and throughly cleaning them MIGHT be all that is required.

Then again it could just be a warped rotor and you are tripping on the power washing thing.