A question about common mode noise
BNC (with coax cable) and Common Mode do not go in the same sentence. 

Common mode noise is talking about a signal current being passed round a pair of wires, be that as a differential signal or as a single ended signal with a reference line. Both lines need to be subject to similar electromagnetic fields for the noise to be common to each.

BNC, with coax, is a single signal wire shielded by the return reference. As such the signal does not receive the same noise as the shield. So common mode noise can not really be applied to BNC cables. 

If you want to pass a signal some distance and have the common mode noise removed, make the signal differential and pass it through a twisted pair cable which may or may not be shielded. Alternatively, pass a single ended signal with it's reference through a similar twisted pair cable and use the reference in your receiver.