Ghost rattle...99 M3

It appears to come from the rear seatback or headrest right side (opposite driver in US)
It's not a thump like a rear shock mount...and it's not a loose wheel
lock in the trunk's tool box.
Anybody have experience in this item?
I have unlatched the seatbacks where you can look straight into the trunk and it still persists
The rear window latch is not loose at all and the window is closed.
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wrote:

Seatbelt retractor rattling under the trim? Try extracting the passenger belt(s) on that side and keep tension on them while you go on a test drive.
/daytripper '00 s4 6spd
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wrote:

Just read today that a company here in the UK have developed a CD with various tones that tend to reproduce real sound waves that occur in a car when driven. Preliminary reports mention that getting the right volume helps as too high and the sound is distorted and too low it is ineffective.
www.rattlebuster.com
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On Jul 12, 1:02 pm, snipped-for-privacy@clara.co.uk wrote:

Thanks..... Looked at the link and the CD won't serve a purpose, since the rattle only appears on irregular road surfaces.
David H
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wrote:

So you have made that decision based on what? Body rattles occur at different frequencies and the monocoque of a modern motor car is like a big empty oil drum (Duane Eddy and his Guitar - 1950-1960s)
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On Jul 13, 4:57 pm, snipped-for-privacy@clara.co.uk wrote:

RattleBuster - Will Not: Pin-point "Road-Impact" induced rattles, for example: "A rattle caused by the sudden impact energy absorbed whilst driving over a pot-hole in the road". Be clear about what sort of rattle you are looking for.
Understand?
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