WD-40 is not a proper lubricant, why did you use it? I had similar issue and silicone spray fixed it completely. Again on your pair it could be coming from different place and not from that black plastic hinge connector. On mine it was obvious when I opened the cup, it was squeaking like crazy right there.
On further inspection I actually do think it's the black plastic hinge connector. Guess I'm gonna have to find me some silicone spray if that will apparently fix it.
Edited by starfly - 1/24/14 at 11:59am