This is commonly called Bleed over and usually results from one of three conditions.
- Excessively long runs of wire within the home of non-twisted pairs.
- Loop wiring from phone station to phone station.
- A nick in the phone wire somewhere within your residence causing a weak interconnect between phone lines.
Phone wiring installation today should be done as a home run system, each phone station being a dedicated run back to a common terminal block.
Please remember if you have a problem with your phone wiring within your home, today it is the responsibility of the electrician rather than the phone company as in the past.