What is most likely the cause of the lift station problem given the following known information: 1) low & high level pressure switch is normal, 2) lead pump starts at correct level and levels continue to rise, pump cuts off at correct level, 3) wet well is alternating between excessively high and low, 4) all electrical controls are in automatic, 5) when lead pump runs force main pressure remains the same, but increases when lag pump runs, 6) levels in lift station drops when lag pump runs, 7) Check valve arm remains stationary in lower position when lead pump starts and stops, 8) check valve arm rises when lag pump starts and stops, 9) wet well inlet is normal for dry weather conditions.