In amplitude modulation (AM), we change the amplitude of the carrier frequency. We add the message signal to the amplitude of the carrier frequency. We replace the amplitude of the carrier signal by this sum to get the modulated wave. Now, the amplitude is affected by noise while transmission. This causes the signal to be noisy.

In frequency modulation (FM), we change the frequency of the carrier signal as opposed to its amplitude as before. Now, noise can’t change the frequency during transmission. Frequency can only be changed during modulation. Hence, the signal would be relatively less noisy.