Several times over the last year the whipped cream produced by the ISI whipped cream maker had an very off flavor. Almost metallic. All of the parts were cleaned with the same results.
Bob, welcome to Seasoned Advice. Are you thoroughly rinsing whatever chemicals you use to clean it? Also, are you adding any other ingredients, such as sweeteners?
Obviously it wouldn't be the same bad batch of cream over a full year (although that would certainly explain a gross taste...), but you might check the freshness and flavor of any other ingredients.
Double-check and make sure you're using N2O (nitrous oxide) cartridges instead of CO2 (soda chargers). You MUST use N2O gas! CO2 delivers a metallic (extremely unpleasant) tasting whipped cream no matter how much sugar you add.