615-320-9800

good question as  i just got a call from this nbr as well.

Received 11 calls from this number on 10/10
Thus far today, received 6.

If we pick up the phone, it says to press 1 or 2.  I pressed 2 and it said it would put me in touch with a conversation in session.  After a few seconds, and not hearing anything, I hung up.  

The number I believe is listed under Krell, Inc.  It rings on both cell phones and all home phones.

Got a call from 615-320-9800 (Nashville, Tn). I did not answer. They left a voicemail - from Hireright - contacting me regarding a reference for a potential new hire via another company. I called the number back in the voicemail ... still waiting for return call. I don't see this as a scam - the person in question did, in fact, contact me the day before that he had listed me as a reference.
(had to list call type as "unknown" - there was no selection that fit)

Appears to be legit. They called twice but only left voice mail once. If you call back this number it is Krall or Krell and you are given several options, none of which were clear. However, voicemail left a name and different, direct number. Company was "HireRight" for a professional reference that I had previously agreed to.

I have rec'd 2 phone calls from this # at my place of employment.  First phone call listed someone I knew and left a message.  Second phone call I talked to live person asked for reference on someone I did not know.  I am not calling the number back.