Feedback?

If the oven is earthed correctly it is impossible to get an electric shock ! The earth continuity from the plug or outlet to the casing of the oven should be less than .1 ohm resistance. You need to get an electrician to test this and also to do an earth loop impedence test on the electrical supply. You have a fault in your protective earthing system !! That is one important issue, the feedback could be caused by an earth leakage from the element.

Kenjo
January 2015