Disconnect the cable feed at the entrance of the house, then measure the voltage between the shields from the street feed and and the house. Take care while doing this because there could be an unexpectedly high voltage here. I've seen installations where the voltage is so high that there is a visible spark as the connection is made or broken. If this voltage is significant, you'll need to be anal about your grounds.

You should also measure the voltage between the electrical system ground and the cable system shield. This voltage should be near zero. There should be a wire "bond" between the electrical system ground and the cable grounding block. Simply having a separate ground rod for both is not good enough, the rods must be bonded. Why should they be bonded? Even if there is no voltage difference between the shields, there can be very large voltage differences between ground rods immediately after a nearby lightning strike. If a human or piece of equipment is trapped between warring ground rod potentials, there can be serious consequences.