Severe Noise problem with tenant in adjacent apartmentis building

[N.A N.A]

Took possession of family apartment building in Beverly Hills. Just returned from camping in vacant unit to get feel for property. Discovered severe problem with noise from tenant living in building next door.

Basically a woman with a teenage son and a toddler live in lower level apartment next door seem mentally unstable. They live with windows open and no curtains - toddler is allowed to scream and sing song at mind boggling volume. Mother drops f bomb and talks back to her in loud sing song voice. Mother sings at full volume (decent Whitney Houston voice) at all hours - I documented with smart phone 11pm, midnight outbursts of song, or toddler allowed to bang and scream for 5 minutes to be let in to bathroom. Bath time is a nightmare. Sound penetrates with doors and windows closed and new air conditioner on.

Seems my tenants have been dealing with for over a year - first we have heard of it, but apparently last summer adult male occupied also and fights would last to 4pm nightly. Tenants have called police and child protective services in past. Then a dog was apparently barking non stop and tenants called police and it has been removed. In the past when tenants knock on her door they are insulted and threatened.

I called neighboring apartment owner and even though she is 2 months late on rent he is scared shitless to do anything and he continues to accept rent when it is sent. I told him I would consider holding off on improvements to my building and selling if nothing could be done, however he is scared.

This situation is severe - I purchased a thousand dollars of trees to attempt to create some sound buffering and I am having new windows installed.

I am really conflicted as to prospects for investment. My ability to fix up tired units and get market rent is questionable and I don't know if I could rent vacant unit out for market rent without being misleading to new tenant. I also feel challenged to ask for the next 10 percent rent increase from my existing tenants who have been living through hell?

Other than working with a non emergency code enforcement officer - which may result in vandalism and retribution from mentally unstable person - any help would be appreciated.