Personally I'd just keep your SSD and SATAs drives going - why change?  "Going back"to SCSI is a gamble as you'll be looking at second-hand drives (I'm assuming - new are crazy prices), which won't be as reliable and as used vary wildly in their noise output.  A 5 - 10 year old drive has reached it's end of life and the older, the noisier as bearings fail.  15K drives are never quiet, nor will they have had an easy life.

JB