Ok fixed it!
Fastforwarding to the answer for anyone finding this in the future...
I removed the lid and hinges (ref maintenance/service manual). Easy job, just a few screws.
Found most of the noise was where the hinge brackets attach to the cover. They move a bit and creak like mad. I carefully(!) removed the brackets from the cover, applied Teflon spray lube onto the mating surfaces (see pic), and reassembled after it dried. Silent.
Found minor noise on the hinge "pin" itself, so applied some Teflon spray lube there too. Reassembled everything and it's mint! Never been this quiet!
Note the Teflon spray can go everywhere so best to do it off the printer and immediately wipe up any overspray. Once dry, any residual is easily wiped with a dry cloth.