I bought a refurb a1224 with year warranty from macbank in UK. great machine and now running 10.11. I have a 1.8" HDD plugged into the imac. however for last few days it randomly drops the drive. I get a message in top corner of the imac which says I did not eject the drive correctly. Drive is still plugged in. Why is it dropping my drive? It is not a time machine drive just has data on it.