Grinding noise from brakes

Hi all – Disc brake Noob here looking for a bit of advice. I've got Hayes Stroker brakes fitted on my new bike. After riding today (3rd time out on it), the brakes are making a pretty horrible grinding noise when freewheeling, not when braking.
I did go through some pretty big muddy puddles so I'm hoping that it's just some dirt on the pads – just wanted to check that it was nothing more sinister.
Cheers

Does it disappear if you give them a quick on/off squeeze to clean them?
Usually works for mine if they get gritted up (remember, a good squeeze will be pretty effective so make sure you are ready for it!)

Happens all the time when the pads get wet, should sort itself out when they dry out.

Thanks for the replies. I only really noticed it when I gave the bike a quick clean after my ride so I didn't get a chance to give 'em a squeeze at speed! Fairly sure they'll re alright now though.
Any recommendations for disc brake cleaner? Cheers

Fenwicks/Muck off!

hosepipe or riding through streams always seems to shift little bits of grit around & get them rubbing – should go soon after you next pull the lever if that's all it is

unlikely that you need brake cleaner