Tenants Complaining About Other Tenants

[Ryan Denman]

I have a rental house in Colorado which is a 3/2 ranch on the main floor and has the basement finished as a 1/1 with its own entrance.  While I lived there renting the basement was a nice bump in extra income and the tenants who lived in the basement apartment were pretty easy going, aside from an occasional marijuana small in the house (I allowed them to smoke in the backyard).  My family moved out of the top floor and into a townhouse and now rent the top floor of the original house separately from the basement.  Things were good for a month or so, and then the top level tenants started complaining to me about marijuana smells.  I went over on occasion to verify the condition, but there was not a lot of evidence of it.  I suggested the tenants communicate between themselves to resolve the issue.  Another month goes by and I get complaints from the downstairs tenants about high levels of noise in the early morning, issues in the laundry room, and constant badgering via text for the upstairs tenants.  

The house is not "designed" as an up/down duplex so a fair bit of noise (music, walking, running, voices) can travel between floors, as well as smells with the shared ducting for the house.  The tenants upstairs are 6 months into a 1 year lease and the basements tenants are on month to month.

What are some good ways to handle the situation?