hi all, i'm new to this forum, i've just bought a 1996 chevy astro day van it's a 4x4, when i'm driving theres no noise what so ever and as soon as i take my foot of the accelerator pedal it makes a knocking noise the noise goes as soon as i accelerate, no matter what speed i go as soon as i take my foot of the accelerator and just let it roll untill i stop it knocks any ideas please. i've been underneath and can't find anything obvious, i'm thinking gearbox?

 

same prob here....i'm thinking main or rod bearing

 

Start by checking the crank pulley....check to see if the rubber has deteriorated from the centre of the pulley to the outer ring.
Also have a look at the flywheel bolts. You'll have to remove the starter to see them clearly....make sure they are nice and tight