Cat Filter Installation Instructions
Just an update on my situation.
I replaced the CAT filter with a stock (actually NAPA), and just tonite had the noise again. With the stock filter, the post-shutdown air bubble was the same size, and the dribble of tiny bubbles while running looked the same. Tonite, it actually made the noise at idle, and I saw no difference with the bubbles this time, either.
My problem, again, was that I was getting a noise that increased with the RPMs, and usually started just over 2000 RPMs. However, it seemed to only happen when the fuel was cooler than say 70 F. In other words, it would usually go away after driving for 20 minutes or so. Tonite when I listened under the hood while it idled, it seemed like the noise was from the general timing belt area, but I'm not an expert on exactly where that is vs the pump, turbo, etc.
I opened
another thread on this.
1. Would rubber gaskets, instead of copper, work? I ask partly because it seems like they'd seal better, but also because one of the coppers dropped into parts unknown when I was swapping filters.
So I'll tentatively say that my problems with the CAT filter are solved - I still don't know how some folks get no bubbles whatsoever, but I'm satisfied that it's the same with the stock. Now hopefully I'll get this other problem solved, whatever it is.
Once I'm done with the repair shop, if that's necessary, I can get my Golf back to drinking crisp, clean 2µ-filtrated diesel.