Top end noise?
 

Just purchased a 85 944. PO daily drove it no issue till he hit a deer. Then sat waiting for repair for about a year and a half. He only started it to move in and out of garage. Then one day it wouldn’t start so he decided to sell.
Fast forward found bad fuel pump wiring. Drained gas, filled with new. Fired right up. Top end/lifters VERY noisy. I’ve had 4 of these now in the past year and they all sat for at least a year. All of them cleared up rather quickly. This one will not. Note; oil light stays on and gauge stays pegged at 5bar. No milkshake, no smoke, no funny leaks, car was Wel taken care of. Clean. Let it run for about 10 mins hoping it would clear up. Drained oil. No debris, no bad color, no metal shavings. Refilled and put new mahle filter on. Still very loud. Loud enough that I don’t want to let it run long. Idles nice, doesn’t get hot. Drives very well. Any ideas? Can you post video to thread ?

What weight of oil are you using? Too thin of a weight can cause lifter noise. Also, sometimes the lifters take some time to prime if the car has been sitting for an extended period of time. My 85.2 sat for 12 years before I bought it and got it running. I use 20W50 and the lofter noise diminished after about 10 minutes of running at idle.

20w50 and a mahle filter.
Car has ran for over 30 mins. Still noisy. No smoke no shavings in oil, runs nicely, just wayyy too loud

Collapsed lifter(s)?

@walfreyydo. Maybe. After a year and a half ? I’ve had barn finds that quieted down after not starting for 5 years.
And without performance issues ? I’d imagine I’d see some kind of damage/shaving/performance issues

Easily happens if sitting over a year or more. I get clacking lifters if I park over winter and do not start the car a few times. Takes 20 min sometimes for them to refill and quiet down. Best to let it idle and not rev it up.

what if you run it on thin oil, drain and fill with proper 20w50?
Mine was loud for many days (10-15 minutes each time), then, It stopped. I changed to proper 20w50 oil after that.
After inspection of Camshaft Housing, I found that previous owner used cheap, paraffin-rich oils, and, because of that, the internals are covered with dark brown "film". I also removed hydraulic tappets and pushed on those small buttons to make sure they move.
Note: my car was sitting for about 7-9 years. On first start the engine was SO noisy, that I almost fainted!

Running a light weight oil like Mobile 1 5w-30 for a few months could help clear out deposits. Running an oil flush could help even more. However in an old engine this will probably cause seals to leak and also cause some bearing wear. Seals will eventually need to be replaced anyway. Rotting rubber in a 35 year old engine is a given. Also make sure your radiator hoses are in good condition or replaced. If one bursts it could cause major damage.