When we have extended periods of rain I have noticed that the basement starts to smell musty and the walls become damp. Is this a sewer-related problem?

Not normally. In our experience we have seen more often than not that the home-owners roof drainage is not directed away from the house adequately. Usually the ground becomes saturated and pushes moisture through the walls. This problem can usually be addressed by putting extensions on the downspouts that are long enough to take the water away from the immediate area. In some cases, it becomes necessary to construct a “French Drain” around the perimeter of the building and send the water to a sump somewhere away from the foundation.