It is not possible for me to know why a specific individual has a catchy tune in their head. However, it is common for people to have songs or melodies stuck in their heads, also called an "earworm." This phenomenon can be caused by a variety of factors, such as hearing a song repeatedly, being in a good mood, or even stress. Additionally, the way our brain processes music can make certain melodies more likely to become stuck in our heads.
What are your thoughts about this?