I am surprised that swapping out the ABS spacebar with a PBT one eliminated the spacebar rattle. The simple swap did not eliminate spacebar rattle on my RF87U or HHKB. However, I was able to virtually eliminate spacebar rattle by swapping ABS with PBT, installing a Silencing Ring on the spacebar switch, installing foam pads under the spacebar, and lubing the spacebar stabilizers and spacebar switch guide rails. I used Superlube grease for the stabilizers and Superlube 51010 oil for the switch guide rails.