I've experienced similar 'tingles' with a couple of modern appliances at customers homes during my work and have always wondered what's behind the cause. It seems that construction of the appliances would explain the occurrence in most cases from what I have read posted here, but the potential for it to be lethal is of concern, especially to those with no knowledge of how these things work! I'm going to isolate the whole circuit and see if the buzz persists and will report back with further findings. My belief is that it's harmless but I am going to check all the wiring to see if it's sound. I put the unit up myself and the stud wall it's on including first fix cabling, so I'm sure it's not cable damage. I can bring in a friend to check for leakages but would also like to know how I can remove the buzz using bonding if the fault is capacitor leakage.
Thanks to all for the great and useful info.