Legal Question in Landlord & Tenant Law in California

Landlord is breaking the warranty of habitability. Give them written notice and chance to correct the problem. you need to document the proof (of notice and of the problem). If it becomes a legal issue, you will need to prove that the disturbance as alleged by you, did happen. And if it goes to court and the disturbance and noise is considered considerable, you won't be liable for the lease.

I sometimes wonder how Madan passed the bar exam. There is no breach of the implied warranty of habitability in the situation you describe. AND a breach of the implied warranty of habitability does not get you out of a lease. What you have is a possible breach of the covenant of quiet enjoyment of the premises. That doesn't give you a right to break the lease either. Your remedy is to sue the landlord to force them to take action and for damages, which generally would be the measure of the difference in the value of the premises with and without the noise. Even with the noise the property has some value to someone, even if you don't want to live there anymore unless the noise stops.

Whether legal action would be a good idea depends on how well you can prove the existence and degree of the problem. Madan is right that you need proof. It also would be best if you escallate the issue in steps, starting with a formal written demand that something be done, followed if needed by a threat of legal action. If htat still gets you nowhere, then you may have to consider court action.