I recently had the bearings go out on the fan bracket in my '92. I could hear and feel the vibration when the car was at idle. Opened the hood and could see an intermittent "slow" of the fan when car was idling. I took the drive belt off and spun the fan. Instead of coming to a gradual halt, the fan would slow abruptly, so, bingo!, bearings in the fan bearing bracket were junk. Car was also at 258k mi., with the last tb/wp at 119k, so I went ahead and did it all. Car runs like new, just have to replace windscreen and figure a fix for old, cracked seats. I told you all of that to tell you this: my suspicion is that your problem is worn bearings in the fan bearing bracket. Best of luck!
In my case, the noise was a lower tone than the engine at idle. It was intermittent, with associated vibration. That is to say: the engine would hum along as per usual at idle and then the engine would feel and sound as if it were "bogging down," as if something were applying an undue load to the engine. If I sat in the driver's seat and placed my right hand on the middle of the dash above the seats, I could feel a noticeable vibration during the "bogging down." What was happening was that the bearings on the fan clutch bracket were so worn, the fan was unable to turn freely and smoothly-trying to stop turning, even. That, in turn, was placing more load on the drive (serpentine) belt trying to turn the mechanical fan and causing the engine to work harder to rotate everything, thus the "bogging down." It was not constant , but came and went (department of redundancy dept.?). When I removed the drive belt from the fan pulley, I was unable to appreciate any undue "play" or "wiggle" in the fan, but the fan would not rotate freely. How can I put this? It was like there was a tangle on the middle of a yo-yo string, such that the yo-yo doesn't unwind smoothly. Also, when I applied a decent amount of throttle between 35-45mph, there was a noise and vibration like when you thumb-shuffle two halves of a deck of cards together. Sorry for the length, but that is the best way I can explain. I hope this helps in some way.
I feel your pain. Replacing a drive belt on your '94 should take no more than 1min30sec. That's about how long it took me, and I don't goof with cars for a living.(I goof with them like it IS my job, though)