The first thing I'd look at is the cam lever, best case that area needs a light oiling, the gear and cog thing that rides on the shaft are sintered bronze, so it absorbs oil and self-lubricates. If its dry, when the cam lever is holding the cog out of the gear, it my squeak as it rubs, also it may be worn out, letting the cog rub against the gear, but usually this is more of a clicking sound.