After parking my car last night, I heard a buzzing noise from under the hood. There was a thread on here a while back about the ABS getting stuck in the "on" position and buzzing until the battery dies, so I suspected that. Opened the hood and sure enough, it was buzzing like mad. One poster replied that tapping the module with a screwdriver would shut it off, and sure enough it did.
Goes to show that reading Subaru forum threads on problems you don't (currently) have can come in use eventually.
-Matt