Do you have a telephone network interface (Grey Plastic Box) on the outside of your house?
If so open up the Customer side remove the phone line and plug a phone into the jack.
If the static goes away the problem is with your house wiring and the phone company will charge you to come out. If the static is still present then the problem is with the phone companies lines and there should be no-charge to correct it.
If the problem is with your house wiring, check for loose connections at the jack and the network interface (make sure the screws are tight). Also look at the wires to make sure they look to be in good condition and that there is no excess wire, where the insulation was stripped off.
One other thing if it is a wire problem in your house...
If your phone cable has 4 wires (red green yellow and black) and the yellow and black are not being used, you can try to swap the green wire with the black and the red wire with the yellow.
You will have to make the swap at the phone jack and the junction box. If it is a bad wire in you house this may help clear up the static.
Since you have 2 phone lines the green and red wire may be for your phone line and the yellow and black may be for your modem in which case this will not work. It all depends on how your friend installed the phone line.