I was wondering what had happened to you and your situation.
You have re-proven first handedly a previously known phenomenon called "grease noise".
Grease is basically oil with a thickener - industrial gravy to some extent. Different greases use different thickeners. Depending on the physical propeties of the grease and/or its thickener, it will do different things under different conditions. Grease thickeners include sodium nitrate (nitrite, I can' recall which), clay, PTFE and other agents that slipped from memory long ago.
Some are quieter than others and some are flat a$$ horrible for noise. You may have inadvertently gotten a grease that is not as quite as some other alternatives.
A/c's used in machine tools are often EASILY over lubed. Depending on the speed, these bearings only need 20% to 30% of the cavity grease fills (how much is 20% of a very irregular cavity is VERY hard to determine). For continued high speed, you can go as low as 10% or 15%. When you're using such low/precision fills, you don't simply slather in the grease like you might pack a wheel bearing for a coaster wagon. Not hardly.
In precision fillls, you literally place/insert the grease in the groove and around the balls and in the ball pocket in the cages with a syringe. You then slowly rotate the bearing to distribute the grease evenly. Start ups are slow and pulsed that get longer and longer in duration. If you put in too much grease, ball skidding can occur. If you try to run balls out from the get go, skidding can occur. If a p poor, wrong, unlucky grease choice is made, the damn things can squeal and howl horribly.
Viscous drag can/will cause overheating. Sometimes, simply running the bearings at low speed to channel the grease will alleviate the problem. Sometimes, you have to wash out the grease and repack it with the syringe method. Sometimes, you have to use a different grease because some grease are just plain "noisey" and only a different grease will fix the problem.
I wasn't about to bad mouth your grease choice as the grease you chose to use or were given to use is DEFINITELY a premiums grease. However, as your experience clearly shows, it may not be as quite a grease as you might wan to used.
What would I have used/recommended? I've been out of the industry too long to keep abreast of the latest in grease trends. I recall that grease suppliers in the USA and Europe were NOT as noise sensitive as the Japanese grease makers are/were at the time I was involved with bearings. One company that did a LOT of grease noise work with the bearing company I worked for was Kyodo Yushi.
If they have an agent in the USA, they might be the company I'd call to try to find a quiet machine tool bearing grease. Otherwise, your guess would be as good as mine as to selecting an alternative grease with lower noise potential. As far as fill percentage is concerned, that too is often an empirically derived value.
Keep in mind that the less grease you use, the less tolerant you'll be toward contamination and/or life extension.
If you're bound and determined to run at high speeds, oil air mist might be the preferred option. Or you might simply try going to a "dry sump" fed lube system wherein DEXRON III were jetted or drip fed to the bearings. We went this way on some previously grease lubed dynamometer bearings and NEVER had another problem with them after going the DEXRON route.