That is hot believe or not. That is actually not acceptable. Re-formatting your HDD could help. Sounds like it is starting to die. If it possible and you wont lose data. I would try a format. Then go from there. If it keeps acting like that. You are most likely due for a new drive. Also you may want to try somehow to get better airflow to it. Maybe bigger fan, moving the drive if you can.
Try to keep your HDD between 35c and 45c. At 55 you are at or getting close to the mas temperature for that device.