It varies a lot. Some MBA do have relatively quiet trackpads, while others can be disturbingly noisy. The same goes for MBP, although they seem slightly less noisy than MBAs on average. But it's a lottery as you might get a quiet trackpad in either MBA or MBP, but I think more common to get a noisy one than a quiet one. It can be annoying if you get a loud trackpad. Consider returning your MBA if it bothers you a lot.