Originally Posted by
Micheal Blue
... The bike shop says that unlike BF or Brompton the Dahon uses a vertical hinge - thus there is more stress on the hinge, thus more chance of creaking. BF's and Brompton's horizontal hinge apparently forces the hinge shut naturally, thus there isn't as much stress on it...
That is it in a nutshell. However the creaking is indicative of dry metal to metal contact so your Dahon's hinge may actually need to be taken apart and lubricated instead of just being tightened.