Five0stang106

Ok so I have a 01 a6 2.8... I have had a lot of work done to it in the last year, and the last thing I was messing with , was the exhaust. It ended up shutting off on me one day. After that I cut the patch job on the exhaust off and replaced the cats and 02 sensors with new ones and had it all welded back up good as new.. so I get it back and it's nice and quiet but now I notice it has a nasty tick coming from the driver side valve train ... I checked to see if maybe if jumped time, and it seems to be in time still, I have to take the crank pulley off to check for sure but what i can see it seems to be ok.. so whats the next problem it could be? I'm so sick that it's broke but I'm scared to start digging into the head... please help! I need some advice