Also it could be many other things, phone techs working on the line, making cable cuts etc. You may have a wireless handset - porta phone, and other porta phones close-by are interfering at times.

I do not know about Canada, but in the U.S. , everyone has an 'interface box' outside where the home wiring cross-connects to the telco line. The home owner is supposed to go out ( if he has phone problems ) and open the box, unplug the telco line and plug in a telephone and test his line there, if he gets dialtone etc and can dial ok, then he has house problems, and to repair that the ph co WILL charge, but if he can not dial or hears excessive line noise, etc, then that is the telco problem and they will NOT charge.
It pays to have a $9.95 walmart special elcheapo phone just to test with at times of troubles to isolate the problem as yours or theirs.

Hacking your line would require a physical connection somewhere close by, and it would take a court order for the Telco to legally tap your phone, in that case you would not hear or suspect a thing as it would be done in the CO. Normally by one tech and none of the others would know about it.

Personally I suspect some type interference.