Has trouble starting sometimes

Started a while back, tried to start, made a horrific grinding noise, died instantly. 2nd try, fired right up. Got less then a mile when I noticed my voltometer dropping rapidly, made it home exactly when the battery died completely (5 miles) diagnosed as a bad alternator. I replaced the alternator. Voltage problem fixed, car started and ran fine. After a while, the started started to make an odd noise I'd assume is a grind It is a loud noise but does not sound to me like metal on metal grinding. It happened on every start. I replaced the starter. Started and ran great, most of the time. On the old starter I did notice wear on the teeth that looked as if it was not fully engaged on the flywheel and seemed to be barely touching, I thought due to lack of power from the bad regulator inside it. One dirt road later and the problem came back, tightened the connector on the new starter, fixed, sort-of. Just every now and then she has trouble starting. Seems unrelated to engine temp, outside temp, number of turns before the engine starts (sometimes she does not want to fire on cold cold mornings and refuses to start untill I turn the key back to accesory and retry starting), and does not seem to happen at any frequency. Sometimes it happense once a week, once it happened twice in 5 mins. The only correlation I see is a lower then usual reading on my voltometer, Usually around 13v or so when it normally reads 14. I'm wondering if this sounds electrical, like a bad connection or decayed wire somewhere, or just a cold weather problem. I have yet to test the theory fully, but as I recall all occurances recently have happened while i've had less then 1/2 a tank of gas, so I was also wondering if it could be related to fuel pressure in cold temperatures and the noise being the engine turning with no fuel.