My car's been doing this for a while now. It only happens in certain RPM ranges and in certain gears (usually ~2200-2450 RPMs and 2nd/3rd gears). I've checked the transmission fluid level a couple times and it's good. I've read other places that it's possibly caused by the torque converter but i'm not sure how to test/confirm that. I know my TC fluid has never been changed so maybe that would help? I forget if sport mode eliminates the problem or if I just shift differently than the car does so I don't see the problem. I'd love to make it stop as it's rather annoying, but it doesn't seem to really DO anything...

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2003 X5 3.0i, 150k miles