You said new suspension arms, did you do/check the lower balljoints on the front when you had the arm off?

I just did all of my front suspension and found the inner track rod ends were toast. Like half an inch play in each side! So may be worth checking them Out. Only a 20 minute job each side, but will need an alignment after! To check these jack the front up at one side to isolate the rack with the weight of the car on one side, then grab the elevated wheel at 9 and 3 o’clock and push in an out as if you were turning the wheel. Mine was physically clucking about, but even a small amount of play will cause vibrations! My inner ones were perfect and new.

Engine mounts are potentially another component to check, you can check these by getting someone to turn over the engine while you watch and there shouldn’t be excessive movement as the engine starts. Also you can stand side on to the block and rock it side to side and you shouldn’t get much movement out of it if they are good.

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E53 3.0d Sport 119,000 Miles
E61 535d Estate - Hybrid turbos and Dark-side intercooler...389hp,792nm