A written complaint that lands
Put it in writing, keep it factual, and save a copy. A written complaint creates a record showing the landlord knew about the problem — which matters if you later need to show the landlord failed to act.
Send your complaint by text, email, or letter. Identify the source of the noise (which unit or what equipment, if you know), describe what the noise is, and list specific dates and times with how long it lasted. Explain how it interferes with your use of your home. If the noisy neighbor is another of the landlord's tenants, you can note that the behavior appears to violate the lease.
Be clear but professional — avoid insults or threats, which can distract from your point. Ask the landlord to address the problem and, if helpful, suggest what would resolve it.
Keep copies of everything and note the dates. If the noise continues, send follow-ups documenting that it is ongoing. If the landlord ignores repeated, well-documented complaints about a tenant they control, 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.