Electric shock / vibration from sockets

[Superhoop77]

When I charge my iPad from certain plug sockets at home the metal back vibrates with a static kind of electric shock.
I don't think it's the iPad because it doesn't happen from every socket. Any idea what this might be?
The sockets where it happens is in the lounge which has a spur (?) into the conservatory and it happens in there too. We bought the house last year and had to have the spur checked to make sure it complied with building regs but we got a certificate to say it was ok (paid for by the sellers!)
Thanks.

 

[PrenticeBoyofDerry]

If it's related to the spur supply and load side. I would do some investigating at those two outlets, isolate circuit first, prove the circuit is dead and look for loose connections or damaged or burnt cables within the accessories.