On my Saturn 2003 Ion, the starter makes an extremely loud noise upon turning key in the ignition. The problem is recent and literally sounds like something is going to disengage or break. Otherwise, car starts right up.

If the noise is coming From the starter then The starter has Failed..Try tapping on the starter lightly while someone holds the key in the crank position and see if it starts

Check for other loose heat shields.
The shield you removed would allow more noise to enter the cabin too.

bad motor or transmission mount.

A/C getting old,no oil.

That sounds like battery--wiring-or starter. Check the battery voltage. It should be 12.6. volts with engine off. Clean the battery terminals.

Without hearing the noise, it is hard to diagnose. If you replaced the bearings and the noise level is correlated with the speed of the vehicle - I'd look at the wheels/tires. They may be out of balance or you could have a radial shift in one of the tires. Rotate the back tires to the front and front to back. See if that changes the pitch or noise level.

I would check the ignition switch. When it doesn't start, I would check to see if you are getting power to the starter when the key is turned to the starting postion.

fan loose or bearings going

there should be a valve that prevents the fuel from traveling back dow the fuel lines when the vacum is lost. make shure this is working properly

sounds like the steering wheel was turned sharply one way or the other when you turned off the key...turn the wheel in the oppisite direction while turning key to take tension off the steering wheel lock