F2-420 Red lights and "Checking file system..."

[username8181]

So usually I turn off my NAS when I won't be using it to minimize power consumption and also to avoid data loss in case of a power outage (disks are on RAID0 and I don't have an UPS currently).
But recently whenever I turn it on the HDD lights are red and a "Checking file system" message is displayed for 5-10 seconds before it lets me log in normally and continues to work perfectly as if nothing happened.
I haven't noticed anything weird after it finishes the checking, but this has never happened before so I'm a bit nervous if everything's okay, according to TOS everything's fine with the disks and all my data is there, so I don't know what causes this checking...
I believe this started after I updated TOS (right now I'm on version 4.2.06, a few moments ago I saw there's a new release so I might update later), before that it started up directly.
I'll greatly appreciate your help!