Few people experience this, although some excipients (non-medicinal ingredients) can at times create a metallic or bitter aftertaste.
It is possible that some people react in certain ways to one of the ingredients or, more likely, to some of the non-medicinal ingredients (see the back label) used to help with blending in capsule and absorption. It could also be a combination with other supplements or medications one takes. When we receive such feedback we make sure to pass on this information to our formulators. If this persists, you may want to consult your health care professional.