Another thing that happens with older houses, and why the multiple earthed nuetral system was brought in is the earth connection can go open circuit (joints failing or going resistive with age) so all the EMI rejection caps in modern power supplies will be leaking a few mA on to this earth wire meaning you can get a zap / tingle
though i would not normally recommend any of the general public play with an outlet, you can check the AC voltage between earth and neutral with a decent multimeter to see the difference is almost 0, if its not, you have an issue,