Same here, just got 2 calls, one in the morning, one in the afternoon. (Conclusion, they - robots - follow up with a second round, OR someone who has hacked phone numbers (so many out there!) sold to two separate spammers/scammers!
No ID. ("CO, USA"), several reports on record of no human, tones/noises. Seems to be auto-fax spam. Calling my do-not-call registered phone - twice - as if they care.  Report & block, probably the best that can be done.

Call came at 11am. Just tones. Blocked and reported.

Now they are using the number to just text people who are selling their vehicles online saying that they sent you a certified check in the mail. Only texts phone number doesn't receive or call out. Scam