The lower end rumble on startup has been reported by a few posters. I read of one who had his engine repaired by MB, The procedure was very long but it entailed opening the engine up, reading the casting nos. then getting appropriate main bearing shells.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)