I've finally got really irritated at the rattlign noise the harness triangle make, especially the passenger one as I usually don't have a passenger. The harnesses are properly tightened up, but the triangle moves on the spacer thingy.

Fixed it by undoing the bolts and putting a piece of heater hose cut slightly too wide over the spacer. Redo the bolts et voila - the triangles are now damped by the rubber, but are able to move if necessary.
Rescued attachment 2006-08-26 3 ST harness mount noise damper.JPG

Seat belts normally have a wavy washer to stop rattling.

My harnesses didn't come with anything like that, just a spacer that the triangle fits over, but is locked down by the bolt. The gap is about 8mm, hence the rattling