My 2006 Chevy cobalt started making a loud taping noise over heated and the clutch pedal kept going to the floor and back up on its oun. I've never seen anything like it. What can cause this

sound you have a blown clutch slave cylinder

Anytime the a/c is turned on the cooling fan will come on so that the engine does'nt over heat.It will not turn off until the ebgine has colled down.

Well, you size the wrench needed for the bleed valve on the slave cylinder, mounted on the transmission housing 8 or 10 mm in most cases. Make sure the clutch reservoir is full, and kept full. Then you'll need a trusted assistant to work the pedal-one who will understand the reasoning and procedure behind bleeding a hydraulic system of air trapped inside the lines-it hinders hydraulic pressure on the clutch fork to make the clutch work at all. I say trusted because you dont wanna make it an unpleasant experience (I've participated in quite enough of those videos!) Patiently explain that the clutch pedal should be depressed slowly and steadily to the floor after you have opened the bleed valve and kept depressed to the floor until you have closed the valve. So just as the pedal starts traveling down, open the bleed valve, fluid is forced down through the line and out the open valve. Best if you close it just before the pedal reaches the floor-as soon as pressure is let off, air has a chance to re-enter through the open valve, so close it quick. A couple of times should do it-when you have a steady stream of fluid, no more air, and you know the line is bled of any possibility of air, then finish tighten the bleed valve, not too tight. Check the reservoir again, and take your trusted associate to dinner.

Dead cell and or loose grounds at the starter will do it every time!!

There can be a couple things, nutral saftey switch, AC DELCO, NEUTRAL SAFETY SWITCH Direct Replacement Part For OE Number 24219476 `$68.67 , ignition switch not adjusted correctly, try jumping the starter at the starter to see if the starter is working, of course I have just fixed a car that the guy didn't have the shifter in park, try these things and get back to me

Check the heat shield over your catalytic converter, see if it's loose.

Slave cylinder is what compresses the clutch, the black plastic piece your talking about should pass throughout the firewall and actuate the clutch master cylinder.

can be anything if noise while driving cv joint-hub [wheel bearings] exhaust hanger broke -transmission- brakes-if while idling[engine knock] rod-pistion

its either your front brake pads or your CV joint is going bad .. Jerry