Let's look at these sentences:
Rain falling on the roof is making a noise.
This is an observation about a particular instance in which the rain is making a certain noise. You are saying that there's a specific sound caused by this rain. You could also say: The rain falling on the roof is making a noise.
Rain falling on the roof makes a noise.
This is a general observation about how rain makes noise when it falls on a rooftop. It's not describing a particular time, because rain does not have the definite article the.
Rain falls on the roof is making a noise.
Rain falls on the roof makes a noise.
These two sentences are grammatically incorrect. They are considered "run-on senteces," because you have to use the conjunction "and" to join two phrases together. For example: Rain falls on the roof and is making a noise. You can read about run-on sentences here: https://academicguides.waldenu.edu/writingcenter/grammar/runonsentences