What did the mechanic who did the work say?

 

After keeping the car for a couple of days and performing a cold start, they think it's the belt tensioner on the other side of the engine. I'm going to get that done just so it's a wear item I won't have to worry about later, but I don't really believe them. I'm looking into getting a second opinion but finding a mechanic that'll touch timing chains is difficult in the Brisbane area. I might just have to bite the bullet and take it to VW directly.

 

If there is a problem with the timing after they did the chains, its defiantly worth moving on it sooner rather than later. That said you should be able to look at that accessory belt tensioner on start up and hear the noise to decide for yourself if that's the problem you hear.

I know when I used to keep my 3.6 CC in the garage 5-7 years ago I'd hear the injectors and lifters on startup and clacking was loud and quickly went away (15-30 seconds). That's why I didn't weigh in. The mechanic should be able to determine the noise or get a second opinion. Even in the USA my master tech friend at VW says he rarely comes across 3.6 issues so I understand being able to find someone who knows what they are doing is tough. Meanwhile the 2L is a dome a dozen issue because of the number of those engines sold.

 

An update:
I found a Euro specialist mechanic 10 minutes from where I live so I booked it in. Prior to taking it in I decided to change the oil/filter because it was due anyway and to see if that would help smooth things out with getting proper tension to the chains and whatnot. after filling the car the rattle/scraping noise almost completely went away save to a slight noise that lasts 20 seconds or so, which has remained the same since (it's been about 3 weeks at this point). when I took it to the shop, they kept it overnight and performed a cold start and tried their hardest to hear any worrying noises but came up with nothing. they also reported to me the alternator pulley was becoming noisy so that would have to be changed soon.

when I went to pick the car up, they got me to start it up with them so I could point out the noise to them (the car had been sitting for around 6 hours so it was as close as it was going to get to another cold start). when I started it up I pointed out the greatly diminished but still present noise coming from the chain side, after they listened for a few seconds they determined that it could be a bad PCV. I replaced the PCV valve and gaskets myself about a year ago with one of those RKX kits you can buy from amazon/ebay, and although the installation appeared to go smoothly, there's the possibility it was faulty or I accidentally damaged it during installation or I didn't install it properly. I've decided to just replace the whole valve cover as it's not a huge expense. I'm also hoping this'll help reduce the emissions from my exhaust since a properly functioning PCV should let less oil into the intake.

for reference, below is a link to a video of what the noise used to be. for some reason the microphone in my phone isolated the noise and made it sound a lot more prominent, but it was still very loud in person prior to changing the oil.

 

It’s so tough to diagnose with a phone for sounds. Sort sound like my engine and no issues but at the same time it sounds like it might be an issue. If the shop isn’t concerned and there are no codes then I wouldn’t worry about it.

 

I ended up taking it back to the euro shop as I had developed a leak from the sunroof (that's also now turned into a massive can of worms that I'm still dealing with months later). They ended up keeping it long enough that they were finally able to hear that noise.

They still determined that it isn't chain noise which I believe as there have been times where the noise has been delayed, and in that time the engine sounds perfectly healthy. They've told me that they reckon it's flywheel noise that is non urgent but will need to be addressed at some point. They've quoted me about $2k (Aussie dollars) to get it fixed. I'll probably end up doing it as this is something I'll need to have sorted when I go to sell the car.