Could be a cam pulley or timing belt tensioner or a stuck valve or a noisy injector too.
My 00 ouback has a little clackety clack going on with my timing belt pulleys or the left side valvetrain. The other day it was louder than the rod knock my WRX currently has. Scared me to death so I shut it down. It was gone when I started back up.
If you don't have gold flakes in the oil then I bet the bearing in one of the pulleys on either your accessory belt or on the timing belt is going bad or you're just experiencing the normal farm tractor valve train sounds subie motors tend to make. I feel like the noises get louder with thicker oil too.
There's a few videos on youtube where guys with belt/pulley ticks put up that might be good comparison.
Also, if it's any consolation, the ticking on my outback got much louder just after switching to Rotella, I'll be switching back to high mileage Pennzoil on the outback as a result. Rotella despite being 5w-40 is much much thicker than a regular 5w-30 when cold, it really should be rated 10w-40 when used in gasoline engines with lower oil pressure IMO.