I can hear a person on my mac has this happened to YOU?

Question

     Ok this is really strange but 3 days ago I was sitting at my imac typing away in word for mac when all of a sudden I could hear someone (like a but dial on a cell phone)  I listened for a bit and started yelling "HELLO" but they could not hear me the only program that was running at the time was finder and word for mac.  I called Apple tech and talked to a tech who told me he had never heard of something like this happening before.  We were on the phone for about 30 minutes all the while the person I heard was still on my imac. I could hear cars racing by like their window was open and the sound was VERY clear.  Funny thing is I live in the country and my road is silent during the day other than the occasional mower noise.  I could also tell that they had hardwood floors because every now and again they would walk across the floor and then bang something on a desk or counter or something.  I kept hoping the phone would ring so I could hear a voice or name so I could tell them my imac could hear them.. (it was like a baby monitor was built into my mac) ... they never answered the phone as it never rang, but I could hear them turning pages, sighing and breathing....
     It was creapy. I called my daughter as she is a mac techy type and let her listen to it and she couldnt figure it out. The Apple guy could hear it but not figure it out. I called a friend who has an imac to see if she had ever experienced this and still no answer.  Now today it did it again, and as I am typing this I can hear this person walking around, cars moving by the open window at fast speeds, turning pages, sighing, breathing and banging on a surface of some sort.  It has been on today about 4 hours and now is sort of creapy and annoying at the same time.  Anyone EVER had anything like this happen?  It starts out of the blue and I can reboot and it is still there... but it stops as mysteriously as it started, yet sounds like they may be near a laptop because I hear a click like the top of a laptop being closed then they are gone.  WEIRD....
Someone has to have experienced this before, but I have searched the net thinking someone would say something but I find nothing no matter how I word my search.
Anyway, any suggestions or comments would be greatly appreciated.
Oh and incase you need to know I have the following Apple products:
Ipad 3 (1 in home)
Ipad 2 (3 in home)
Iphone 4s (3 in home)
Apple TV (4 in home)
Mackbook pro (2 in home)
One could say I am a fruit tard as my kids friends call me. We are Apple all the way.

Answer 1

Ok the answer to Shootist007
I have cable internet and cable phone yes
To Mike Sombrio
I changed the frequency of the wireless router with the Apple tech to no avail and we changed it a few times.
To Csound1
Surprisingly the sound was not affected by the volume controls and the weird thing is I even tried playing an Itunes music track to overide the sound that was being made and it was playing but I could not hear it ... it was like this thing just toook over my mac. I could not hear the music and going to youtube same results could see it playing but no sound other than the creapy breathing.