Happened to me too starting around 47k. I have done my own oil changes every 6 months between 6,000 and 7500 mile intervals using Mobil 1 filters and 0w 20 Subaru oil religiously. Switched to Mobil 1 EP 0w 20 oil and noise increased. After 1k miles on the new oil and filter I changed oil but not filter. Noise continued; after 1000 miles I Added 10 oz Rislone boy did it get louder and more constant. This weekend I drained the oil out with 1000 miles on it (300 w the Rislone additive) and it looked like crap. I assume something broke free when I switched to M1 and the added Rislone did something to clog the filter. Changed the filter and upgraded to Castrol Syntec 10w 30 and the noise is much quieter at idle (almost gone) and very low at cruising. I am in New England. Car calls for 10w 40 and 15w 40 in other markets!!! May go that route. Suspect the 0w 20 is too thin.
I have been wondering for a while .. which has more damage? .. starting an engine to idling for 10 minutes with a 10W/40 oil in a 20 deg C ambient temperature or driving for 1 hr in a 95-100 deg C engine operating temperature with 0W/20 oil.