I have a WD7500BPVT, I have used 3 donor. There is weird stratching noises sometimes. Sometimes head tickling as dead head. I had to image in this condition . Because drive had opened before in another DR attempt. Modules overwirited. So much bad area in SA. I dont want to touch SA. till imaging %70 .( Risky . I know. ) and 3 hdd died.
Now using 4th donor head. I have tested SA modules. Ofsetted some bad modules to good area (MTR offset option . This option not work properly. Trying to read modules from bad area. Its dangereous. And writing this module to new adress. You have to open it and change with a good one. Lucky to copy1 modules were good. Used them). And weird stratching noise gone now.