It has to be pretty bad in order for them to fix it. Mine quiets down after 5 minutes or so. Wastegate replacement is pretty expensive because they are so hard to reach. May was well replace turbos at that point.
Under CPO, they don't cover "noises or rattles" so it's a touchy subject. If you're looking to buy the extended warranty to cover the wastegates, its a real toss up =/