Strange noise like chirping birds in the engine

This reminds me of what it sounds like when you have a worn belt. They tend to squeak as they wear out and get louder, and they need to be replaced anywhere from 30,000 miles to 60,000 miles, generally. It's not a serious problem, and it will probably get louder. It is best to have it looked at before long to make sure it isn't more than just a worn belt, and you'll avoid more trouble if you replace it sooner than later.