4 Wheel Parts Wholesalers is having a sale right now on BFG muds and Pro Comp muds and all terrains, buy 3 get 1 free. Hard to beat that. Saw the ad in their customer magazine Off-Road Adventures, Dec 2000/Jan 2001 issue. If you need a discount order code, mine says 912.
Other possibilities are Goodyear M/T-R (supposed to be good), Bridgestone Dueler M/T & A/T (I've run 4 sets of these and love them), Mickey Thompson Baja HP (ask Matt Adams), and the new Parnelli Jones Dirt Grip (don't know much about these, pictures look cool though).
It all depends what you're looking for. Muds are louder than A/T's, but not objectionable. You wouldn't see so many people use them if they were. A/T's are a good choice if you don't do anything serious offroad. The other guys vote for BFG A/T ko's, and for an all around tire, it's a good, safe choice. That's why they sell tons of them.
One way to look at it is: GO FOR IT. Get what you want. Heck, it's only money, and they'll wear out in a while anyway. If you want a mud tire, get it. The Pro Comp model is a good price and I heard performs well. It has siping on the lugs also.
Any popular mud tire, like the BFG or Bridgestone or Pro Comp, is louder than a A/T but shouldn't vibrate any more than a A/T, since they're all built on the same carcass, only the tread pattern is different. You will have to rotate them more though, the more aggressive the tread, the greater the frequency of rotation to keep them wearing even, especially with the Explorer front ends.
Man, I'm long winded. Hope this helps some. If not, at least my fingers got some excercise. Good luck.