Wonky volume increase

Is it my 3-4 yr old Phonacs, or my iPhone? Sometimes when I am on my cell phone, it suddenly sounds like someone kicked the volume way up and I am in a steel 55-gallon drum. It is very loud and echo-ish. I tried shutting off my rt HA today when it happened, and that seemed to help. The wonky noise sometimes only lasts 10-15 seconds, so it is hard to know why it leaves when I try something. So; is the HA going wonky, or is the iPhone interfering? Thanks.