I'd pick up the phone or try and make an internet connection and ..... nothing there, but the line sounded open.
I went through all the procedures suggested by the phone co. to no avail. I had them out to the house twice. The phone co. could never do anything about the problem but the service techs where strangley sullen and almost hostile.
I even bought a new modem. No good. I got a new puter with another modem. No good. I started talking into the dead phone whenever this happened. I could tell the line was open. The phone sounded like there was someone at the other end. You know, those little hollow electronic, barely audible clicks and buzzes. I would tell the $*%)!*@&#$%$*@&@#$! jack booted thugs on the other end whenever my phone wouldn't work what sort of farm animal they probably were presently cohabiting with. I also explained to them they were wasting the taxpayers money as I was only a tax paying, conservative voting, keyboard commando. It took awhile but the phone rarely has the no dial tone problem anymore. Either they gave up or got better equipment.
I'm no telecommunications expert, but I have a couple of years in residential alarm systems.
This sounds like a classic case of either; a loose or dirty connection at the service box or at a jack.
Or a partially chewed wire, with the culprit being a rat.
You don't know how many $350,000+ houses that I made service calls to for this very reason.
You don't know how many looks of shock I got when I displayed rat chewed pieces of wire to owners of said houses.
You don't know how many times I heard," It's impossible for rats to be in my house", as I am looking at the landscaped back yard ending in to thick woods.