Do not peremptorily assume the landlord will do nothing about your complaint. Talk to him. If you are a good and long standing tenant, believe me he will listen. Keep in mind, the landlord is responsible to all of his tenants' actions on the premises if they interfere with another tenant's quiet enjoyment.
If your landlord fails to resolve your problem, you have several remedies which include withholding some of your rent or terminating the lease. All remedies are highly fact dependent, so you must familiarize yourself with the rights and liabilities that flow with each remedy. The easy way to do this is consult with a knowledgeable attorney in your area.
I completely agree my Mr. Easlick.
In addition, if the landlord is unable or unwilling to help, you have additional oprtions.
Since the City of Los Angeles has strict rent control, you should also contact the Los Angeles Housing Department for advice and information on how to handle the situation:
You should see if local law enforcement or the housing department will assist you in speaking with the tenant and gaining access or use a free landlord tenant mediation service.