My 69 Dart w/ 9" drums did that also. On a cross-country drive I thought I heard squeaking on turns so had the front bearings replaced in AL. I watched the mechanic and he backed off one notch from finger-tight as I do. In north MS, the left outer bearing failed, with inner race "welded" to the spindle and outer race spun in the hub, ruining it. The bearings fell out in my hand, so the hub would slide off. Luckily the shop I limped to had another 9" hub in their junkyard of cars out back. They also had the county's best welder who heated the race cherry red, switched to pure Ox and burned a slot down it, then chiseled it off while still glowing. Didn't mar the spindle at all. I was back on the road in one hour for only ~$75. The right side failed 5 years later, also ruining the hub. I don't know if cheap bearings or a generic problem with the 9" hubs.
If your hubs are toast, I would consider switching to or disk brakes or at least 10" drums. Both require different spindles, so don't fuss if your 9" ones are toast.