As title: when I press the brakes after driving some time in the rain, there's a distinct "moan" first time out. They then proceed to wobble nicely. They work well enough. It's sporadic. 

Yesterday drove home from the airport, where the car's been outside for 6 days, and the judder is definitely there from 60km/h / 40mph. 

 

I figure a good first start is to do multiple stops from 100km/h to 25 or so and scrub them clean. That should indicate whether the discs are warped or it's just crud (I do tend to do 400km at a time and don't really use the brakes much - not much traffic and few turns will do this for you). But I don't understand the moan. 

 

Any thoughts?

 

 . Bret

Crud.  Surface rust / corrosion.   Discs or pads or both. 

 

Look at / inspect the brakes.

Servicing pre or post winter is a good idea, strip, clean  and grease.

and brake fluid change recommendation is at 3 years & then each 2.