When a hard disk is not working properly your Synology NAS, the DiskStation will detect this and start beeping and when I say beep I mean beep a lot. I had a problem with the fan on my Synology DS211+ and it took sometime before I could diagnose the problem to be the stupid broken fan so I had to beep of my DiskStation, so I would not have to hear that awful beep sound. After that I shot down my DiskStation and replaced the fan.
If you have a Synology NAS with RAID configuration 1 or another RAID configuration where at least one disk failure can happend you should be fine otherwise it gets complicated.
You can find this excellent guide from Synology on how to repair the volume on your Synology NAS if needed.