Are people listening in on our phonecalls?

is there an expert who can shed light on a troubling question which has been bugging me lately? every time i am on the phone to my family who live some 25 miles from us. when i can be talking about random things all of a sudden out of nowhere can be between 5 or 10 minutes of the conversation the volume goes up on the phone it sounds louder and echoey , i can hear myself can be ok to one person but not the other. and sometimes the same happens to them it really strange theres also a faint background tapping noise sort of tap tap.... tap tap... rythem its weird . is there someone trying to listen to our conversation or not? i just dont understand how the phone can be totally fine to start with then change the nex and be back to normal again. what do you guys think?? does it happen to anyone esle?