bob the rattle might actually mean it is the motor mount or engine shocks. This is especially true if the engine is not clearly missing just shaking. If it changes when in gear especially reverse almost garanteed to be mounts.
m

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Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)