Injector/engine Nailing/knocking noise when cold

My wife's '13 Passat experiences a knocking/pinging/nailing noise when the engine is cold. It gets worse with more throttle. If the engine is warm, there is no noise. It's very much like the noise in this video:
https://www.youtube.com/watch?v=tRGn9DZ3ZkI

It started out mild a short while ago and has steadily gotten worse. I don't drive it often, so I didn't know it was getting worse. The engine actually felt like it was stumbling/missing when I drove it yesterday.

I experienced none of this after the car had warmed up, only when it's a cold engine.

Does anyone know how to identify which injector is causing this? Also, is swapping an injector in the CKRA engine as simple as it was in the ALH engines? Would I have to do any adjusting/calibration via VCDS if I swap an injector? (I'm pretty well versed and mechanically inclined, just not able to find much on the new engine.)

I've also heard some discussion it might have to do with a throttle valve of some sort, but I'm not extremely proficient with this engine.

Any help is greatly appreciated.
Noise from this thread:
http://forums.tdiclub.com/showthread.php?t=436724&highlight=cold+injector+knock

and from this thread:
http://forums.tdiclub.com/showthread.php?t=472394&highlight=cold+injector+noise

From other reports here, the nailing noise is caused by a bad fuel injector. I don't know what's going wrong with them specifically, but replacing the injector solves the problem.

try diesel purge first- but do it the right way by pulling the fuel filter cap, suck it dry and pour a entire can of diesel purge in. put the cap back on and fire it up, rev it up a time or two let it idle for at least 2 minutes to get the purge threw the rail, but no more than 5 minutes as the purge is getting diluted by the second. Shut car off and let sit overnight and the next morning it hopefully will be knock free. Purge works if let soak like this, oh and I also mix in 1 oz of 2 cycle oil to lubricate the hpfp as the purge is lacquer thinner dry

I have not seen much success with using Diesel Purge as described above. The fuel pump will dilute it so rapidly that it doesn't have enough time to be effective.

I prefer to run the car exclusively on Diesel Purge (by running the fuel supply and return lines into the bottle) until all of the DP has been consumed by the engine.

This is an old how-to from back in the ALH days, but a similar rig could be built for a commonrail. It might need to be done from the tank's lift pump rather than from the fuel filter - I don't know. http://forums.tdiclub.com/showthread.php?t=87948

It just occurred to me that I don't know what the lubricity of DP is and what effects there may be of running it straight through the high pressure fuel pump. Does anyone have any input on that?

Once in a while on a cold start I would get some light nailing when the temps were below 25F. I would shock treat my fuel with a lot of diesel fuel additive, like a whole pint bottle. Sometimes I would have to repeat this a few times before the cold start nailing would stop.

This method worked eventually and is a lot cheaper than replacing injectors.

My take on the cause of the cold start nailing is that because the CR TDIs have a lower compression ratio (16:1 as opposed to the 19.5:1 on the AHU/1Z,ALH/ASV or 17.5:1 to 19.5:1 on the PD engines, depending on the HP rating of the engine), and that winter fuel is blended with a lot of low cetane kerosene, the cetane rating of the fuel is on the low side. High cetane makes a huge difference in cold starting and smooth running.

Had a first for my car today. Didn't drive it for a few days and on start I went to move forward and it stalled. Restarted it and it had a dead cylinder even with the rpm raised some. Lasted for about a minute and a half and then cleared up. 135k miles with regular power service use

Was this problem successfully resolved?

I experienced the same problem and ended up with 2 injectors replaced under the extended emissions warranty. A scan with VCDS showed codes that identified the injector with the problem. I think the code was for something like "Torque difference for Cylinder 1."
As described, it was only a problem when the engine was cold. The dealer probably won't do anything unless the code shows up when they do a scan.

the individual cylinder adjustments to timing and fuel don't happen when the coolant temperature is below 50C

That's why it shows up when the engines are cold and smooths out as they warm up.

I damaged an injector and it made that terrible hammering nose. I replaced it and even drove it a week before I got VCDS to change the code. Might get lucky on easy removal. I had to use a slide hammer

replace them

I had similar problem. Sourced OEM injectors from Marietta VW for $135each, including o-rings and copper crush/seals. Had to buy a Schley tool for pulling them out. Recoded/adapted new injector IDs using my copy of VCDS and it worked wonderfully. Mileage back up into 55-60s, no more noises.