Here, ponder a few things:
1) after this car began running (what was described as....) weaker-in-power....and was making the loud noise......did you ever set the crank at TDC, check the placement on cam timing (slot), and pin the fuel pump?
I ask because, if whoever did the work did not get the camshaft sprocket absolutely CLEAN with brake clean as well as the tapered fit inside the cam sprocket (these have to be absolutely clean and free of any oily substance in order to maintain the interference fit)....the "hold" on the cam may have slipped and you are now lightly touching several of the valves onto the top of the pistons as that engine rotates.....rendering the endless noise.
I, personally, go beyond the standard torque on the cam bolt as my experience with the older 1.6 engines showed that it is safer beyond the 33 ft. lbs. of torque normally listed. Of course, if you tighten too much....you snap the cam in the first 20 miles and life gets dark...unless, of course, you longed for a different car. I generally end up around 38-40 pounds range.
An out-of-time cam can reduce power....so, think about this.
2) after the pump timing was viewed on the graph....then you ran the car....and the current problem surfaced.....did you ever go back with the computer and re-check the graph? The mechanic may have NOT gotten the three fuel pump sprocket bolts tight enough.
When I had my problem with the newly-acquired 231,000 mile alh Jetta last winter, my engine did NOT have the typical tap-tap-tap generally associated with a "bad" lifter. What it had was a resonance in the upper engine which literally seemed to "swing" like a pendulum back and forth across the block as it ran. To complicate matters, it would STOP doing this and run perfectly EACH time the engine reached right at 165 degrees.......just like someone had thrown a switch.....or, an electrical component had snapped alive.
I also had profuse smoke until it reached the 165 degrees. Once the engine reached this temp on the ross-tech coolant reading..the engine ran seemingly perfect and very strong.
I changed out the N108......swapped the fuel pump, swapped injectors, installed a new coolant temp sensor (twice), installed a new Bosch fuel temp switch, and cut the electrical loom open to the fire wall to check for breaches.
I had attempted to get help on this forum and waded through pages of non-help. Finally, I went ahead and installed a new set of INA's and my life right-here-in-River-City was absolutely great.
If I were you, I would ponder the two points above. The whole idea of loosening the separate fuel lines is not to play a xylophone and check for "tones." It is to loosen one line and introduce a "miss" to that one hole and see if there is any change in firing.
If the injector is working....the engine misses on that hole. If the injector was problematic, no additional miss is introduced.
Good luck....I'm out of here...................
