| I generally find this happens when the rear ride height is set too high, but you usually notice at walking pace as the front sort of flops around.
Best bet is definitely to have someone help you with setting the suspension up for your weight/height/style. Why spend £x000 on a bike and not chuck another £60 getting it right? Try a search on the site for suitable folk to help out.
Cheers,
Ali | 
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