Tim please follow Seans' advice you may have a potentially lethal situation there. I presently ground all of my stuff, but I wouldn't hesitate to lift grounds as required to eliminate hum that can't be cured in any other way. Just always be well aware of the 'potential' for personal harm, which in your case does definitely exist; BE CAREFUL! If you measure with a voltmeter between those 'tingling connections' you'll probably read something close to 100 volts. Try reversing some AC plugs while trying not to induce any hum. If that doesn't help then try an inexpensive isolation transformer like Francisco uses; do a search for membername = Psychicanimal; he has posted on the subject.
