I'm guessing you have mud behind the brake pads, pull it all down and give it a good clean. If that doesn't fix it then attack the bearings (simple/cheap stuff first). Could also be a seized brake piston from the mud, so try to ascertain if there is any movement of the piston with brake application (with brake pads in place and on the disc.

Any chance mud could have gotten into the wheel bearings through a dislodged old vacuum line on the back of the knuckle???

People do the right thing and replace the hubs with the manuals and dont bother to pull the vacuum lines off the back and plug the hole. Hoses rot/get caught, water + dirt + mud = noisy bearings.

Glue a bolt into the end of the nipple that takes the vac hose on the knuckle. Pull all the associated bits away and do a similar theing to the vac supply line from the manifold.

The hub itself (the bit you buy from Warn) will not make any noise on its own if you can fully rotate the dial to the locked/unlocked position.