Does a sound from the anus, which may be a gurgle, invalidate ablution, whether it is heard only internally or also externally, and what is its cause?

The emission of gas (wind) nullifies ablution, whether it is accompanied by a sound or not. Hearing or smelling are not conditions; rather, it is the knowledge of its emission, based on the hadith (definition): "He should not depart until he hears a sound or perceives a smell." As for hearing gurgling in the stomach or merely a sound, it does not nullify ablution unless the emission of something is confirmed. The cause of the sound should be referred to medical professionals.