Microlights are noisey to an extent, however since they can fly at 100mph and the new 4 cylinder 4 stroke engines are much quieter, there is a concern if you are flying near a flying field, that you won't hear them approaching, especially if you are upwind of an aircraft. They have the same rights as anything that has a pilot in the cockpit and you'll need to be careful because quite often they are flying low for some fun, but generally are up several thousand feet for most of the flights.
The problem is that the trike/Flex-wing type are more or less open cockpit and a hit in the body or face at 100mph will cause injury to the pilot and possible complete incapacitation. Therefore, do be very careful if you are flying near an airfield. Even the 3-axis fixed wing type have rather thin windshields, and many have tube and fabric wings which are a little more delicate than a metal wing, in a collision. It's best if you visit and speak with the head flight instructor, or whomever is in charge of the airfield and work with them, regarding your flying.