Why am i getting a knocking sound from engine

Get someone familiar with Subaru (old ones) to listen to it. IF it's lifter noise do a few more frequent oil changes and try adding a pint of MARVEL MYSTERY OIL with each change. IF it's main or rod noise , again , might want to do several frequent(500 miles) oil changes and possibly up the oil weight a bit (10-40) and substitute a pint of MARVEL MYSTERY OIL for a pint of oil. I've heard (and a long time ago owned one) them sound horrendous (compared to non-pancake) for 50K plus. The only thing that would worry me with yours is that one word you used ---'turbo'.......Good luck.