Beyond normal living noise
Repeated loud music and parties can go beyond normal living noise, and you have several possible avenues, depending on who the neighbor is and local rules.
If the neighbor is another tenant of your landlord, their lease very likely includes rules against excessive noise or disturbing other residents. Reporting the pattern to your landlord in writing gives the landlord grounds to enforce those rules. If it is severe and ongoing, it may also affect your right to quiet enjoyment of your home.
Local noise ordinances often set "quiet hours," commonly overnight, when loud noise is not allowed. For serious late-night disturbances, local police may be able to respond. Documenting each incident — date, time, how long, how loud — strengthens any complaint.
Keep your reports factual and avoid direct confrontation if it could become unsafe. A pattern of documented disturbances is far more persuasive than a single complaint.
If your landlord will not act on repeated, well-documented disturbances by another tenant, a free, confidential review can help you understand your options.
This is general information about California tenant rights, not legal advice. Every situation is different.