do me a favor, crank it, leave in park, press brake and give it some accelerator at the same time WITHOUT spinning tires. if you hear the ticking/rattling noise its more than likely exhaust manifold leak. Have someone else walk around front end while doing this with their ears listening at the front fender wells.
put it back in park, then rev it up. if you dont hear the same ticking, i can almost say it IS exhaust manifold/