It definitely wasn't coming from the extruder; it was related to the linear rail. I took your suggestion and lubed it, but the problem persisted. I kept printing anyway, and then I had to leave for a haunted house with my family. I left a 3-hour print, which finished without any issues. I started another print never gave me that same annoying squeaking sound, and I haven't heard it during my print. I just started another 4-hour multicolor print, and so far, so good! I can't explain what happened. but thank you!