OK, i replaced the oil pump gasket AND the radiator...

I asked a Subaru tech about this for my aunt's Subie. Mine doesn't make the ticking noise (until it warms up) but her's does. I thought it might be something like worn valve lifter but he said that the pistons are actually looser (more free play) in her model. That noise is the pistons rattling in the cylinders until it all heats up and expands. I don't recall what the excuse was for greater piston slap other than maybe using aluminum in the heads (which has a larger coefficient of thermal expansion). They want to lower the mass of the heads to improve fuel efficiency.

To reduce mass, the cylinders are an aluminum compound. Aluminum expands and contracts more than iron. When the engine is cold, the aluminum piston is smaller in comparison to it's iron cylinder in the block. The hollow sounding piston slap occurs most when you start the engine when stone cold. As the engine heats up with running, the aluminum head expands more than its iron cylinder so the tolerance between head and cylinder diminishes with heat up.

I've heard the following used as a test to check for piston slap. First thing you do after the car has been sitting for many hours, like overnight, is to start the engine up but let run it for only 15-20 seconds while listening to the sound. Turn off the engine, remove the spark plugs, squirt in a little engine oil, reinstall the plugs, and start the engine again and listen. If the problem is cold-starting piston slap, the noise will be significantly reduced or gone after adding the oil but only for about another 15-20 seconds (until the oil has been blown out).

The lifters on some of these tend to get air in 'em and pump down. Not sure which years did this, but getting air into the opiling system can cause it.

Dave

Seems to have subsided. I ran the car for a while yesterday, and for a while today, and the horrible noise has gone away...knocks on wood and crosses fingers...

It would do it a LOT on warm days, and today is over 65, and it's not doing it, so.....