Sorry to say, I was getting a bit of that growling a couple years ago. It think it was happening when turning, I don't recall it making noise when going straight though. Dealer replace the rack & pinion under warranty - no more noise. I always wondered what that would have cost if I had to pay it.

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2002 E320 4-Matic
2008 Subaru Outback
2009 Subaru Forester