I finally had time to listen to your post. The sound was similar, but different. The 3 tones were in succession, one after the other, about 2 seconds each, over and over for about 45 minutes.
Could it be an alarm tone at a place of business? Such as at the Valero refinery in Memphis: they have alarm tones for fires, weather, H2F acid release, etc and each alarm had alternating tones.