When any brand of drive hears a dreaded cod it usually points at the eventual failure. Take a look at the age of the WD drives there to see why this is being seen. I've been using WD drives for a good long time and as yet have to see one fail or even start clicking. When you do hear a drive with a clicking sound it is generally the read-write head bouncing off of the drive's magnetic platter or disk inside. Drive heads depend on air flow while the disks are spinning inside to keep them a short distance above where they hover until the disk or disks(internal) stop spinning.
there was no important data on them. i was just curouious, but all of a sudden cod started, this happend on western digitals and only on them