Also drive a 2.2 and to have suffered with the tap tap noise i first thought it was the lifters so treated with wyns after an oil change no joy so removed the heat shield only to find it was cracked. Had this welded but still no joy then after a proper look found that i have the first stud on the underside of the manifold had completely come out along with the insert. After asking about having it repaired told it would be ok providing all the other studs came out freely not some thing i wish to ponder on so i just put up with it, soon goes once engine is warm so for now at least it can stay.
PS if any OOF members are up for having a go at repairing it for me say maybe next summer i am more than willing to cover the cost.