Answer: There are three possible causes of noise on an IP340. First, the analog common must be connected to the common of the input source. This is even true with differential inputs. See the instruction manual for a diagram. Second, all unused inputs must be connected to analog common. A input left floating can drift above the input range and break down the channel to channel isolation. Third, you must keep your source impedance low.(less than 100 ohms)High source impedances when exposed to noise leakage current can result in significant noise voltage at the inputs.