Hi sarak,
First of all, congratulations on the success of your manchego! A cheese to you on that. Second, how old is this sour cheddar? Most cheddar types really need to age a minimum of 3 months, and personally, for all the work that goes into them, you really should age them out to 6 or 8 months. If you waxed it early (as in before it was 6 to 8 weeks old), it's quite possible that the sour taste is because the whey that is still in the cheese from the make, and which normally evaporates over the first while, is now trapped in the cheese. You might find the cheese is wet under the wax, if so, it's not finished drying out. For a cheddar, if your cheese is still weighing more than a pound per gallon, that extra weight is just trapped whey and it needs to dry out more. Anyway, if it's heavier than it should be, then I recommend removing the wax, aging it in a ripening box until it weighs somewhere in the vicinity of 1 lbs per gallon of the make. Then, if you want, wax it, and continue to age it until it is at least 3 or 4 months old. Then see how it tastes. Even if it's not great then, rewax it and through it in the back of the cave and forget about it for awhile. Find it sometime around Christmas and see if it's gotten any better. Some cheeses just need a lot of time to come into their own.
- Jeff