Radiator Leaking and Loud noise coming from the engine.

The Check Engine light is telling you the Engine Computer detected a problem and set a diagnostic fault code. Your mechanic will read that code to start the diagnosis process.

You never solve a problem by adding something to the cooling system. Those chemicals might plug a leak for a little while but you'd never want your mechanic to fix your car that way. The radiator should be repaired or replaced, then the cooling system should be flushed and refilled with new antifreeze. Over time acids build up in the coolant. Those acids will eat through radiators and heater cores. If that is what happened to the radiator, that's due to lack of maintenance and you'll continue to develop leaks. If you've kept up with maintenance, the leak could be due to a rock hitting the radiator. In that case they can usually be repaired.

Engine noises also indicate a serious problem. Continuing to try to drive it is only going to make it worse, so of course it's going to become an expensive repair. You can't expect the engine to fix itself and the noise magically stop.