ooh…that may indicate a scratched platter. Only other shot is to do a swap out of the enclosures. It’s pretty straightforward-just open up both cases, unplug the hard drives (two cables-the four pinned power wire harness (has a red and black wire and usually to more wires), and the data cable harness (the longer flat cable; make sure that the pins line up as there are some drives out there with different interfaces-ATA, Serial ATA, etc.). It’s likely that if the enclosures are identical the interface types are also identical, but it’s easy to eyeball (visually inspect) this.
This may sound weird, but do a smell check on the original hard drive and enclosure; it may have some fried components; also when you open it, perform a visual inspection of the drive and the components on the inside; if anything looks burnt or melted, that’s bad news.
Hope this helps, and probably goes without saying, but we’ve all learned the hard way; I lost about 120GB of tunage about a month ago…still trying to cope…