In response to your reply;
 No BG, but that "unusual noise" was present. Rather than calling our local PD, spending 2 minutes on the phone describing the situation (before they dispatch), the 45 second delay (at least) before dispatching and their average 9 minute response (dispatch to arrival) I decided to look first. Had it been a BG, (a)it's doubtful they would have heard me coming, (b) I did approach the area cautiously and (c) my 3" .45 wheelgun would have evened the odds considerably. I thought I had a BG when seeing the hood open, but my neighbor's build is easily ID'd even at night.
Wow, you can get 911 there in about 12 minutes for a non-priority call? Y'all are doing quite well. Many major PDs are thrilled to be under 8-10 minutes for a call where somebody is being beaten with a hammer whilst on the phone with 911.
I don't know now many police departments routinely spend much time on "unusual noise" calls. That is so low down for a busy PD that if an officer showed up within an hour that would be good...if they ever showed up at all (not dispatched).