Creaky deck

[Gypsynurse]

Hi all,
So I went and looked at a Bristol 40 yawl yesterday, beautiful boat. Appeared to be very well maintained, bristol condition bad pun! however had approx a 2 foot section of port side deck that creaked when walked on. When rapped with my knuckles it didn't sound different than surrounding areas. So I'm wondering rot/delamination or just possibly the butt ends of plywood rubbing, which still makes me think something maybe has come loose? What a ya think?