Okay, so I have a 1997 cobra, nothing special, cold air intake, magnaflow x pipe, 4.10 gears, 83k miles. I just recently stripped the threads on the inside of the head because I'm an idiot. So I brought it to a local mechanic to get it fixed, I had to get the whole head replaced, so with that, I got it done, and with a new head. Now, all of the sudden it is knocking. I don't know if this is a common cause or if the mechanics or just idiots. Or any other possibilities.