Hi Tess,
I noticed the same thing with my shower last night. It was really strange. i wanted to call an electrician and plumber and get them over and would have been happy to pay thousands to get them to fix it for the sake of my families safety. But i spoke with a friend of mine who is an electrical engineer and he told me that sometimes this happens when you have wiring running close to the pipes that draw lots of current (heaters tend to draw lots of current). The wires emit an electro-magnetic field which will then give off a slight charge into the pipes. That is why is happening. Im not sure how to fix it, which renders this messages 50% useless, but if you come up with an idea, let me know. you can email me at tdamien@chloans.com.au
Tdamien
May 2008