Strange circulator noise

Ken C.

I replaced a leaking bearing assembly on a Taco # 110 circulator today. The assembly was a factory rebuilt unit. I put six drops of lubricating oil in the oil cup prior to restarting the circulator. After a couple minutes, the circulator started making a continuous, high-pitched whistling noise. I put a bit more oil in the oil cup, and the noise went away, but came back after a minute or two. The only thing that quieted the noise was spraying WD-40 on the shaft seal. After I left the job, I remembered that I might have stretched the spring coupling before tightening the allen screws. The new bearing shaft was slightly shorter, so I had to stretch the coupling a bit longer to compensate. I wonder if the coupler being under (slight) tension could have caused the seal/bearing noise. Is it wrong to put any tension on the coupler, or do you think this whistling noise happened for another reason?