Water pump bolts backing out? Huh?

[billschroeder5842]

I had an odd thing happen today to my normally bullet proof 91.

I got in to start the car for my 17 mile commute home and and once running heard a loud CLICK-CLICK-CLICK from the engine. The CLICKS would speed for slow depending on the RPM.

I thought it might be a alternator going bad but further inspection show that not one or two, but 3 of the 4 bolts that hold the pulley on to the water pump had significantly backed out at least half to 3/4 of an inch. Clearly this was the cause of the CLICKS

I was able to put an open end wrench on the bolts and crank them down good. I restarted the can and sounded normal as per usual. I checked when I got home and no issues.

So, what would cause 3 (!) bolts to back out? I keep pretty good tabs on the engine but this one has me confused as it seemed to "come out of nowhere."

Anyone else have bolts back out of the water pump?