The kind of right you are talking about, is referred to as Right of Easement over property, in case that you are not able to enjoy your property peacefully you can file a suit against the infringer of the right to peacuful possession. Meaning, you have a right to enjoy your proprty peacefully, but if any person is obstructing your right to enjoy your property, you can either claim damages or ask for an injunction from a civil court. Further, a DG set is not a device that needs to be placed at a particular place so you can request him to change the location of the DG set.
Also, if you can provide me with the details of the DG set, like make-model, I can provide you with the level of noise emmited by the DG Set and whether the same will be considered by a court to be an obstruction.
In the meantime, you can also serve the builder with a legal notice explaining to him you concern in detail and further, informing him that in case he does not remove or reposition the DG set, within a prescribed time, you will take legal action against him.
You can also contact CREDAI (it is a builders association which includes all major constrcution companies and builders in the country), which may listen to your concern and direct the builder to re-position the DG set, provided your builder is registered with it.
For any other information, please feel free to contact me.