Mine is smooth as butter up to redline, 5-speed manual trans. Unless it is the boxer exhaust note you're referring to, which admittedly does take on a weird ragged sound above about 3500rpm. But as far as engine smoothness, I think I might be able to place a glass of Chardonnay on the engine and it wouldn't move.
Not that I drink Chardonnay.
When Mobil dropped Clean 5000 in late 2011, I switched it to Kendall GT-1 synthetic blend. Could it be the timing chain on the FB making it louder, I have the older EJ25 w/ the belt. Also, the revs are more buttery on the Kendall than they were on the old Mobil Clean 5000. Mobil oils lubricate well but they always seem to make the engine emit a little more metallic noise.
Kendall makes a 0W20 full synthetic, maybe try it on your next oil change it's priced below most other 0W20's (but can be hard to find on retail shelves). I think there is a VOA of it on the Petroleum Quality Institute of America's web site.
Originally Posted By: JTK
Originally Posted By: LoneRanger
3000 - 4000rpm is the sweet spot for a subie engine.
Could be LR. I dunno where peak torque is for the FB20, but I wouldn't say 2.0 or 2.5i Subaru engines are happy revers. To me they sound and feel horrible at high revs.