Why does water taste different boiled in different kettles?

I would like to choose an electric kettle to boil water, however, I am interested to know why water tastes different from different kettles. I am wondering if different metals used in the different kettles, is the difference in taste of the boiled water. Is there a way to test to determine whether the metal interior is making the difference? Are there other reasons for the water to taste different? I have tested different kettles side by side as well as testing spring water, distilled water and tap water. In all cases each kettle tasted different. One kettle in particular always tasted the worst, perhaps like metal is my guess. Yet, this kettle was the most expensive of the group I tested from. It also had the most comfortable design in all respects. I have emailed the company to inquire about the metal composition used and was told that this is proprietary information and to feel free to ask them any other questions I may have!