this is the sound of lifters, they bleed down on older cars whilst sitting for a while - e.g. over a week etc.

what oil are you using in the engine? and how does the breather system look like in your car, bad breathers can cause oil to sludge and gum up oiling galleries.

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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)