Hello, I recently upgraded to El Cap like Im sure most of you have. My iMac keeps making this strange ringing sound almost like a ringtone. I'm not receiving a call to my iPhone or a FaceTime request. There is no notification on the screen and quoting programs doesn't seem to help although I cannot verify it happens with everything closed and just the OS running. I swear Im not crazy but I might be if someone can't help me figure this one out! I don't know if I can upload an audio files but Ill record it next time if I can. I'd say it happened mostly around the same time in the AM and no I don't have an alarm app. Thx for looking