93 Suburban 350 w distributor whine noise

I have an intermittent noise like a whine coming from my distributor I believe. The best way to describe it is it sounds like the sound of a failing old mechanical speedometer - kind of a buzz/whine. I checked the play in the distributor shaft today as I was cleaning the rotor & there was very little - a little bit up/down (~1/8") & hardly any noticable side to side. This comes & goes & I can't find a common thread of ambient temp or engine temp or anything else. It's been going on now for almost a year but I have this fear of it failing & stranding me. Any ideas? Thanks.