You could try using Ubuntu without the restricted driver for a few days and see if the issue persists. If it does not, than we have a starting point.
You should have a look at the HDD's S.M.A.R.T. status using smartmontools.
You could also try to listen to the sounds the HDD makes during these freezes/hangs. :) Maybe it is trying to spin up again?
I thought it was a lot more frequent.
You could try using Ubuntu without the restricted driver for a few days and see if the issue persists. If it does not, than we have a starting point.
You should have a look at the HDD's S.M.A.R.T. status using smartmontools.
You could also try to listen to the sounds the HDD makes during these freezes/hangs. :) Maybe it is trying to spin up again?