Let us take a scientific approach. The song is stored in brain cells, and something is either stimulating or irritating those brain cells so that their synapeses are firing.

Allergies may be the cause. Allergies lead to high pressure in the cerebro-spinal fluid which bathes the brain and spinal cord. One known result of this high pressure is irritability. I am convinced that another result is pressure on the cochlea, which leads to sensitivity to sound. Maybe earworms are another, why not? Try a Claretin tablet or two and see if the earworm goes away.

If the cause is stimulation rather an irritation, then the answer is simple. Go on a nice vacation to a totally different environment.

See how simple?