Had a similar problem under the forward cabin berth on my B36 (2002). It was a design fault I think where the aft ends of the horizontal panels, excluding the portable in fill pieces that enable access to the fore hold, were inadequately supported. It was cured, permanently I think, with a length of 3" x 2" wood cut to length to fit as near as possible right across, and chamfered at the ends to form a beam which then fitted across under the edge of the panels at the aft end of the opening into the forehold. The panels were then glued and screwed to to the beam, while the chamfered ends of the beam were glued and screwed to the forward timber bulkhead of the toilet compartment on the port side, and similarly secured to the half height bulkhead on the starboard side where that bulkhead forms the aft end of the forehold. That stopped the squeak and any possible embarrassment for couples that shared the forward cabin when the boat was out on charter !!