I am having the same problem as you & it happens to me also between 2,000 & 3,000 rpms when I acclerate & go up inclines. I have taken the car to the dealer & they said everything is running fine & it's under warranty but I am still not satisfied so it's going back in on 4/10 so I'll let you know what they try to tell me this time. I have a 05 Impreza 2.5 RS SW with only 6,500 miles so that's why I find this to be odd.