In general I’d advice against running used drives for anything other than testing/experimental use.
Regarding noise, if it is just the fan, check the dust filters and clean if needed, it might also be the fan getting worn out, might be worth looking into replacing it just to be safe, since Noctua is the king of computer fans, I’d recommend starting researching how to replace the fan with a noctua one.
If I was in this situation, I’d get a new hard drive that can fit everything on it, copy all data to it, then format the NAS drives and set up the NAS as new.
However, I’d still keep the new drive as a cold backup of the data.