iPhone gargle noise?

My girlfriend and I were on a phone call and out of no where i hear this sound like if someone gargled, spit water on the phone and at the end it was like a droplet sound and then it hung up. I called my girlfriend back and she asked if that was me, i told her no, but now we’re both freaked out. We have no idea what it was nor what could have made that noise. I mean given that she has bad reception, but even then it was a clear sound. Anyone else had this problem?