When I play music on iphone5s and charging - I get feedback/buzz from noise cancelling headphones

Question

This only happens when charging and using noise cancelling headphones (sennheiser PXC350).
I get a buzz, but if I touch the metal on top or bottom of phone the buzz goes. Electrical interference, if I turn the noise cancelling off, no buzz.
Other headphones are fine that aren't noise cancelling.
Any ideas if this is a fault with the phone?

Answer 1

Likely due to build up (and discharge) of static electricity (referred to as ESD).  Ever scuff your feet on carpet and touch someone else? Similar concept here -- your iPad is getting charged up, probably due to movement against a nice generator like the nylon lining in your purse, and discharging through your headphones into your ears.  This effect is often a bit worse in very dry climates.  Perfectly harmless, but not comfortable.
To test this theory, walk around holding your iPad rather than putting it in your purse.  Any better?  If so, either carry your iPad or put it in something that is not going to generate static charge like the inside of your purse.  Plastics and nylon are good static generators, so keep it away from those.  Leather, silicone, rubber, etc. are pretty low generators, and pretty insulative to generators outside of them.