DIAGNOSIS That's usually residual taste from the cleaning solution, or sometimes from a new machine if you didn't do the initial flush correctly.
FIX Run a water-only flush cycle. Don't use any cleaning tablets. Go through the normal cleaning mode steps, but instead of adding a cleaner, just use fresh cold water in both the side tank and the internal reservoir (if you're using the water line). Make ice and discard the first 2-3 batches completely.
IF THAT DIDN'T WORK Check your water source. If you're using the side tank, are you using filtered water? Tap water with high chlorine or mineral content will make the ice taste off. If you're using the direct water line, consider adding an inline filter to the supply.
HEADS UP Never use vinegar or any cleaner not specifically made for the Opal (like the GE brand cleaning tablets). Other cleaners can leave a film or taste that's very hard to flush out of the food-grade plastic and silicone lines inside.