I spent a long time tracking down a squeak from the rear of my Plus 8 trad. For a long time I thought it must be springs related and greased, oiled and waxoyled away to no effect. Finally I located the source as a loose screw fixing the spare wheel mounting support bracket, the bracket therefore able to rub against the (dry) wood frame.
I'm not suggesting that your issue is likely to be the same thing but simply recording that much time was spent chasing red herrings.
