Rattle noise only when in gear

Recently took a cross country trip to Alaska. Half way there started hearing slight rattle when driving. It has gotten considerably louder. Only hear when in gear, and it picks up speed with acceleration. Goes away when I take it out of gear, even when coasting.
Louder in smaller gears and starts as soon as it goes into gear, even with clutch engaged but increases tempo with speed. Since I am now in the great state of Alaska I do not have access to mechanics so appreciate any help or suggestions.