Vibration when accelerating

[wow]

Hi,
 
recently had the engine rebuilt and quite alot of uprated parts fitted so its alot more powerfull than before,
one new part is a 3 inch downpipe, which might be the problem, as the exhaust i think sits a little bit different.
Its just when i accelerate hard in first gear from stand still and second i get a vibration, i think its the exhaust pulling down by the engine movement due to the hard acceleration causing it to rattle on the under braces underneath the car i think the rear one just forward of the diff.
 
How do i overcome this please or do i just leave it, Harder engine mounts ? or do one of those diff or gear box braces that i have seen about sort this problem out ?
 
thanks in advance
james

[BlitzBoy]

Check its not your rear bushes that have gone or maybe the Exhaust needs adjusting with its hangers