I recently had a problem with my up-until-now dead reliable QIDI Tech 1 which sounded like yours (pun intended). I tried many of the same things you did, all to no avail. Finally, I got out my hex wrench kit and tightened every fastener I could find, including the case connector cap screws. I found that the two cap screws holding the extruder to the carriage were slightly loose, as were the cap screws holding the extruders to the stepper motors. Not noticeably loose in operation, but at least 1/2-1/4 turn loose when tightened. After this procedure, the noise stopped and my prints became better looking. My next task will be to revisit all of the fasteners with a tiny drop of blue Locktite on each to prevent recurrence of the problem. If you try this, be sure to use the blue version, which can be removed later with a wrench...the red version is essentially permanent in this application as it takes fairly high heat to make it release. Good luck!