Cellphone interference or sign of death?

So I was on the phone with my friend last night, both of us have cell phones on ATT and the line cut out. So he called me back and a few minutes later the line cut out and when I tried to call him it went straight to voicemail. So then two mintues later he called me back and was like “did you hear that?” and I was like “NO” and he said he could hear me butthen I faded out and there was a voice with static whispering in a very eerie voice to him and he couldn’t make out what it was saying but it was very angry and aggressive sounding. So we were creeped out but brushed it off as cellphone interference.

WELL the very next day I am on the phone with my doctor and the line cuts out and I hear the same thing, this angry agrressive voice whispering in a very deep voice with static in the background and then it started screaming and banging things.

To be honest I am a little freaked out, anyone have any ideas??