I opening up a wall I came across a conductor which I thought was an inactive circuit that appears to be carrying some voltage.  Here’s the detail:  The conductor is a piece of 1950’s vintage 14/3 romex.  When I ran my non-contact meter over it, it registered as a live circuit. When i checked it with my multimeter the hot, hot, and neutral each read somewhere between 0.3 and 1.2v to ground (the voltage seemed to fluctuate constantly and never arrived at a steady number). The conductor routes into a joist bay shared with a number of other live circuits and crosses over them at one point.  Is the curent that I’m seeing “phantom” voltage from the other conductors or do i need to be concerned?