I am trying to determine what this rattle clanging noise is coming from the underside of my GTC? I notice this only when window is down and when going over bumps, the air shocks are all performing well and no sign of those being an issue, it doesn't sound like a wheel bearing... if one can describe a noise which is difficult its not a rattle, a bang, a squeal, a buzz, .. its more like a loose clanging noise of metal as if something is loose underneath, I just don't know where to begin. I was watching a back and forth video of the Person in Vietnam whom was trying to isolate the noise on his Silver Spur and after replacing sub frame bushings and elements like driveshaft, sway bar... it ended up being the Automatic Door Locks at Low speed malfunctioning. I know that is not the issue, if I knew anything about cars it would be frightening, but it has the sound of a shock bottoming out is the only way I can describe this. its not effecting the vehicle overall but just want to make sure that the bottom doesn't fall off the car at high speed! . I would certainly take it to the Bentley Garage but its two hours away, but it just might come down to this if I cant easily identify what it is.
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The other thing that i have noticed is while driving at 65-70 on freeway the vehicle dips down all the sudden in RPM for no apparent reason at all, I haven't noticed this at lower speeds, just at highway speeds and if someone has tied a tether to the back and is pulling me backwards. Weird and very intermittent

 

Also, If your comfortable with jacking it up, start off with checking all your control arms front and back.