This is what I have done so far.
Removed Drive 2 then restarted the NAS and then reinserted Drive 2, and added it to a new Storage Pool 2 and now letting the system check Drive 2 before creating Volume 2.
Once the above has been done, I will recreate the Shared Folders in Volume 2 and then copy the data across from Volume 1, and then delete Volume 1. Drive 1 will then be added to Volume 2.
Hopefully this will sort out the problem.
The big question is: What would cause this to happen? Would the fact that my NAS is positioned about a few feet away from my TV's sub-woofer play a part?