Dismantle the tweeter as slowly as an old man settles into a warm bath. Look for dried coolant or mis-aligned parts, or little bits of stuff rattling around. It could just be wrecked, so you could replace it with a radio-shack peizo horn(wont fit, you'll have to run some wires outside the cabinet and duct tape the speaker somewhere) until the replacement is found.

If you do get a factory replacemnt, and the same thing happens, you may want to think about doubling up your setup, as what you have may not be enough