I did not answer the call. The message was just backgound noise.

Received 3 calls from this number on July 13, 2013.  Did not return calls as I didn't recognize the number.  Have previously answered message calls that left some, "I got you!" kind of text and then my phone service deducted 8.5 minutes from my time.

Rcvd a voicemail, without my phone ever ringing. HTH do these nimrods do that?

Deleted without listening to.

It's possible you were using your phone or there was brief loss of service and the call automatically went to voicemail.  It is also possible they know the voicemail number for your carrier and used the option to leave a message directly in your voicemail box.  They could have an automated system that spams all voicemail boxes.

listed as missed call.  Called it and got connected to my own voice mail.