Aspects of the invention are directed to methods and apparatus for dispensing liquids to and aspirating liquids from a container. In particular, one aspect is directed to a liquid level sensing system that includes a probe constructed and arranged to be moved relative to a liquid sample, a signal source coupled to the probe to apply an applied signal to the probe, at least one detector coupled to the probe to detect at least one detected signal, the detected signal being related to the applied signal and having a rising edge and a falling edge, and a controller coupled to the detector and configured to detect presence of a noise signal based on at least one of the rising edge and the falling edge of the detected signal.