There has to be a source to the noise. As much as we do not know about the deepest parts of the ocean any lengthy research is bound to discover something that is yet unknown to us be it a new species of fish, crustacean, bacteria, or some other deep sea lifeform.
With the rise in technology, it is only a matter of time until scientists discover even more about the Mariana Trench. We know far more today than we knew even just a decade ago, so given more time, funding and resources who knows what scientists might discover in even the next 5 years.
I believe that the chances are so small of finding anything new in the Mariana Trench because most of it has been explored. Scientists have been studying this area for the longest time and haven't come with anything new for years. I think this means that anything there to discover has already been found.
Throughout the history of time, people have had a fascination with things that have seemed to defy logic. In the end, there are usually explanations. Sometimes, it is a scientific phenomena. Other times, it is someone playing a prank on someone else. Ultimately, something is happening to create that sound and it will be found out.