Temporarily disconnect computer and ground cable. Measure AC current from audio ground to that new safety ground wire. Current should be on the order of less than 1 milliamp. Unlike the experiment with safety ground wire, this test actually reports something useful.
Of course that grounding cable will eliminate voltage. Wire eliminating voltage tells us nothing useful. But is that voltage created by a leakage that is too large or by a leakage that is acceptable? You still have not answered a question that determines whether a threat to computer, et al exists.
If your meter does not have an AC amperage option, then connect audio ground to safety ground via a 10K ohm resistor. If the leakage is 150 microamps, then AC voltage across that resistor will be 1.5 volts. If the voltage is less, then the leakage (and need for safety ground wire) is irrelevant. If voltage across resistors is more, than your TV may be a threat to computer and human life.
If leakage is less than 150 uamps, then even a wire about the size of a human hair would have been sufficient to ground out the leakage.
Aga> Here's what I did: Connected TV Signal earth to safety earth directly