I'm replacing a 240-volt split-phase electric baseboard heater. I've shut the power off at both the thermostat and the breaker box. Testing the wires with a non-contact voltage tester shows an intermittent "live" indication on the non-switched wire; it shows a continuous "live" indication on the hot side of a nearby outlet. Testing the wires with a multimeter shows 0V for switched-to-non-switched, switched-to-ground, and non-switched to ground; it shows 120V for hot-to-neutral and hot-to-ground in a nearby outlet.
Which should I believe? Is the NCV picking up a residual signal from the nearby outlet, or is the multimeter somehow ignoring the high-voltage wires?