gelcoat cracks
Surface gelcoat cracking is a common problem associated with the aging process of the resin under years of sunlight and the constant flexing of the deck under your feet or other loads. These cracks are usually slight but, look like hell and sound worse.
Epoxy undercoating and painting is the recommended treatment. Several coatings of epoxy are applied over the sanded deck and then paint. If the epoxy is applied to thin, the cracks will resurface. The idea is to build-up a substantial layer of epoxy to not only hide, but prevent surface cracks. I think part of the real problem, however, is that the deck bends or oil-cans under your feet. The light-weight, balsa-core sandwich construction was supposed to minimize this. My foredeck sounds like crackling leaves under my feet and the cockpit sole is a trampoline. I applied a thin coat of epoxy and paint a year ago and the little cracks are coming back. A brand new boat would cure the problem but then I would have to work every weekend to pay for it.
Good luck!