Will I break my Dahon Mu Uno?
Weight limits are usually based on what the wheels can take rather than the frame. Also like with most things nowadays the manufacturers build in a margin of error so you can likely ride it safely 10-15 lbs above the actual limit.

Riding on compact gravel should not bother the bike so long as you keep it clean - make sure dust isn't getting into the hinges. To rule out any issues with the hinges clean them thoroughly and apply a light coat of quality lube something like Dumonde or Finishline. Then ride the bike and see if the creak gets any better. If it does, there may be some play in your hinges. A good bike shop should be able to adjust that play for you. If it does not get better the culprit is likely somewhere else. Possible sources could be the saddle mount or bottom bracket area.