Hello, A relative of mine has some weird issues with their 2019 Prius. They said one time a message popped up on the infotainment system (not the dashboard) that said "Engine Rat." and it never happened again. They hear the occasional low-pitched, low-medium intensity rattle whenever the gas engine turns on. Not the usual engine running sound. It doesn't happen at start-up. Any ideas on what this could be?