There are a few of things you can do to reduce noise and cross talk.
- Terminate every single BNC input/output that you are not using, with BNC 50 Ohm terminators*. Switch these unused terminals to 'Floating Reference'. This will eliminate the cross talk and reduce the noise. Unconnected BNC connectors tend to act like antennae, thus picking up noise.
- BNC connector blocks are especially susceptible to ground loops. Make sure you are using a common ground.
- Many labs have an alternate power supply line that is clean. (These clean supply lines are not used to power monitors, motors, or other devices that can introduce noise onto the line.) Try to use these power supply lines rather than lines common to noisier electronic devices.
- Be sure to use shielded cables to connect your DAQ board to the BNC block.
BNC 50 Ohm terminators are essentially non inductive 50 ohm resistors. They can be found online and in most electronic parts shops.