Another mod in my quest for a quiet computer. I’ve mounted the hard drive using elastic cord and a cheap auto electrical crimp set. This should reduce vibration / noise transfer to the case.

Use pliers to completely open crimp connector.
Crimp Terminal Opened up

Measure out a piece of elastic and tidy up the ends with a lighter. Thread a plastic cover on to the elastic. Place the elastic in the widened crimp connector so it sticks out just a tiny bit, this will cause it to mushroom-out when crimped. Fold up the edges of the crimp connector with the pliers then crimp.
Crimp

Slide the plastic cover on.
Crimped Closeup

Repeat as needed
Attache to drive

Elastic should be stretched just enough to keep the drive held in place.

Hard Drive Mounted

This could be implemented in a number of different ways depending on your case