Figure i would add to this as well, as i recently had the same issues as others in this thread.
Problem started off with a weird grinding noise that would only happen when the car was accelerating, didn't matter how hard, noise would often start at around 2k rpm and stop around 4k rpm. Also only happened when the car had been driven for a while, 10 - 15km's would usually set the issue off.
Initially i didn't have any check engine lights, but something to me didn't seem right. I immediately checked oil levels, they were fine, so i was a bit confused as to what the problem might be.
Not sold on the fact that the car was working fine, i took the car to a mates and had him check for any error codes. There were no current errors when checked, but there was a pending error code of P0021.
After a bit of research it looked like replacing the oil control valves / solenoids was the go to fix.
I did take the car to a subi dealership's service center to had them look at the issue incase it was something worse. The dealership was close by which was the only reason i took it to them.
Advised them of the pending error code, and of the advice i had found online. They advised they couldn't detect any issues with the car, and they said they found no pending errors. Only errors they saw were something to do with the airbags and battery voltage??.. neither of which my mate picked up with his diagnostic tools. Nor have there been any issues with the airbags or car voltage.. the battery was only recently tested and everything was great. Confused i drove the car home, but still something didn't feel right.
Took the car for a short drive and surly enough, for the first time, the check engine and flashing cruise control lights came on
Checked the error codes again, and this time it was showing P0011 and P0021.
P0011 A CAMSHAFT POSITION - TIMING OVER-ADVANCED OR SYSTEM PERFORMANCE (BANK 1)
P0021 A CAMSHAFT POSITION - TIMING OVER-ADVANCED OR SYSTEM PERFORMANCE (BANK 2)
Figuring the place i had the car serviced were a bunch of idiots (they also changed the oil and put way too much in, i had to drop the oil again and refill it myself, they also over filled the brake fluid and didn't bleed the brakes properly), decided to buy the solenoids online.
Bought them from PartSouq, same parts as Daytona for the H6
Each solenoid cost $57 USD, which works out about half the price of buying them locally from a subaru parts dealer.
10921AA070
10921AA040
10921AA050 (x2)
Arrived in about 3 business days from dubi to perth.. pretty amazed actually for only $22 shipping.
Replaced the solenoids myself as its a pretty simple job, 1 bolt on each solenoid and a plug connector. Took all of 30 mins to change 4.
Reset the error codes on the ECU and took the car for a few lengthy test drives, did a bit of spirited driving in between, and so far so good. The grinding noise is gone, no more pending error codes, and the car sounds and feels much better again. So far done a total of 100km's after replacing the valves.
Going to keep an eye on it closely for a while, but im fairly sure the issue is resolved.
What i would like to know is why the valves failed.. if anyone has any theories it would be great to hear. Maybe i can avoid doing something in the future that will trigger this to happen. Or maybe as with anything mechanical / electrical, things will wear out over time and require replacing.
Hopefully this post helps someone else, i know Daytona's post helped me.