I have noticed more than once that when I travel from Ginger Island to Stardew Valley, the bird sounds and general island sounds stay and override the valley music. It's very noticeable when you travel to the valley when it's rainy and you hear tropical birds. I travel by obelisk, not by Willy's boat. Once you enter a building, and then exit, it goes back to the normal valley sounds. I play on the Steam PC version, the most current update (1.5.4) single player. In my current save, the most used one has mods installed: Configurable Junimo Kart, Better Hay, NPC Map Locations, and the other SMAPI add-ons. I do not believe it's related to modding since I started adding in some QoL mods just recently.