(was Panasonic SA-HT1500, but nobody responded)

9 times out of 10 when switched on from standby, my Panasonic SA-HT1500
Home Cinema system immediately goes into HDD format mode and won't leave
it until said format is performed.

Does anyone have an idea what might be causing this? Could it be the HDD
itself? It was suffering a lot of dropouts a while ago, so I stopped
recording on it pending investigation.
--
Peter