Tried to watch your video link but it said video is private. Since the noise goes away with rpm I'd be leaning towards lifters. 20 psi is kind of on the low side for oil pressure. I'm curious if pressure goes up with rpm. What is pressure when at operating temp? Did you check it with a mechanical gauge or is that scan tool pressure? Probably not low enough to get your lifters rattling though. You could have a collapsed lifter. I've seen just the tiniest piece of foreign matter in the lifter can prevent it from pumping up. If you can shut down individual injectors with scan tool you might be able to isolate it to a cylinder. The noise may change tone doing this.
I'm not a mechanic in a can kind of guy but there are a couple additives I've good had success with.
Sea Foam will remove varnish from oil system. Might free up a lifter if it has varnish built up in it. The following stuff won't effect any ticking but it also works well in fuel system, or when properly introduced through the intake it's great for removing carbon deposits. Just follow directions on can for use in oil or fuel. Getting it through the intake can be easy or not depending on engine. First you get engine to operating temp, run it around 1200 rpm and being careful not to hydro-lock or stall the engine you slowly pour it in. One common method is through the PCV vacuum line. On older engines we would add it through the vacuum hose to the brake booster. Carburated and TBI engines are easy, just pour it through the air horn. Could probably rig up a small hose and funnel and run it through throttle plate on a multi port intake. Once it's in there the exhaust will smoke a lot, it's fine. Shut down engine, let it soak like four to 16 hours then go run it hard under load to blow out the softened carbon deposits.
AT-205 made by ATP is great for slowing down or in some cases stopping seal leaks. Add some during oil changes. I used it first time over 20 years ago on a ford 302 which are notorious for rear main seal leaks. It didn't stop it completely but the difference was significantly noticeable. I used it in a toyota 22R that was leaking at front crank seal. It completely stopped leaking. This product will not damage seals with repeated use. I've used it my personal vehicles and customers on numerous occasions successfully. Several years ago had a customers boat with twin engines, remanned 7.4 mark 4 big block GM. Boat was used for charter fishing and owner was adding oil sometimes daily. A lot of it was the rear mains leaking. You could see the oil pooled up in the transmission bell housing. We started running 25-40 and adding the AT-205 with every oil change. Owner said it didn't stop completely but it made a big difference.
I just went back and read 12 psi at idle. I'd be a little concerned about that. I don't know for sure at what psi the lifters are going to rattle but you gotta be close at 12 psi.