There is a sound glitch when pokeshells eat from a critter feeder in that the sound they make will get "stuck" and loop repeatedly even when they're not eating. It happens without fail every time and is rather loud (not to mention a glitch). It would be like if the portal always made its "new printables" noise even when there aren't new printables.
Listen closely when pokeshells eat from a critter feeder. You will hear the sound glitch of them "eating", this sound byte will play constantly.