Not to be confused with earwhigs, have you ever been plagued by an "earworm" for more than a few miles while hiking? An earworm is a song or snippet of music that runs through your head continuously and is typically difficult to consciously eliminate.
Personally, the rhythm of an uphill climb seems to trigger them. On the first day of my hike earlier this month, I kept having the sickly sweet strains of "The Christmas Song" from "The Grinch" running through my brain. However, after a few days I move from popular music earworms to surprisingly grandiose and inspiring self compositions that I only wish I could replicate when I get back home to my piano.
Here's a good article if you're interested in reading about some of the common earworms and a few half-baked techniques for how to eliminate them.