It just beeps.  I get these all the time from a bunch of different numbers.  I believe that they are faxes.

calls from 604-681-6571 for a number of years.
It trys to send me a fax on my non fax line.

I get repeated call from this and other numbers. just beep-beep-beep. other last 4 digits are: 8158, 5967,6571 and 3371. One research response said it was a fax number.

I get repeated calls from 604-681-6571. Other last 4 digits: 6574, 5967. I got a call last night at 11:45PM!

I traced these 'beep' numbers to an apartment located on 13th Ave West in Vancouver, BC.  Longitude 49.26, Latitude  -123.14 (copy paste into google maps search), unfortunately this only provides a range of house numbers.  The beep is an computerized auto-dialer - first one to answer gets the sales pitch.   The number is a land line.  Can't pinpoint the owner,  because the number is private.  These telemarketers buy up a range of hundreds of numbers - in this case 604-681-XXXX. That's all I've got.  Can't keep  or block them all - as these guys just change 1 digit and they're calling again!    Occasionally I call back immediately and let it ring until it connects - this jams up their auto-dial system for that number  - no one answers of course - if the call goes through, just stay on the line until it hangs up. They've been calling my number for 6 years now, and this is the closest I've come to tracing it.