Noisy Neighbors Complaints - What can I do?

[Matthew Roggenbuck]

Hi,

I have a bit of a frustrating problem.  I own a triplex with one lower unit and two units on the second floor.  Unit 3 upstairs keeps complaining about Unit 1, they pound on the ceiling/floor, they swear loudly, and all around make noise directed apparently up at unit 3. I have spoken to unit 1 several times about this and have also sent out a letter reminding all the tenants that they need to respect the quiet enjoyment of everyone in the triplex.

This has been going on for a few months now.  And every time I talk to unit 1, they say they have no idea about the noise, and it must be the other neighbor. But unit 3 tells me it is from below them, so there is only one unit it could be.  I would evict someone, but it would just be one persons word against another. Do I tell unit 3 to start documenting the noise? Do I just evict unit 1 on the multiple complaints?  Is there anything else I can do? 

Thanks in advance