[Ghostedmind]

when you did the seafoam, did you notice any smoke at all coming from under the hood? that was how i found an exhaust leak (the tapping) if no exhaust leak the it sounds like you might have a rod knocking, which could be a bearing going bad, you need to try to pinpoint the knocking sound a little better than just under he car if you can. if you're saying it sounds like an exhaust leak it may be a bad piston ring. With the information I've seen so far there's a good amount of stuff that it could be.