O-rings on drains are more of what I think is a rattle.

If you are in motion when you experience this then I think suspension,
alignment, tires out of round or out of balance.

It is really easy to check for out of round, and more common than not.

I doubt turbo.

If it seems smooth under acceleration but shaking when braking or slowing please check suspension parts.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250