Get a load of galvanised water tanks/cattle feeders (cheap ebay/gumtree/local tip, , locate next to the fence alongside the trampoline put up on bricks, use a decent drill with a screwdriver attachment (not a metal drill bit), get a few metal screws, drill loads of holes in the bottom, using the same screw until it wears out, far cheaper than wasting drill bits,
add loads of crock, then line with membrane, fill with well rotted manure fifty pence a bag, top coat of cheap potting compost,
Plant with several varieties of the large bamboos.
If you don't like the look of the tanks, clad with wood, willow screening,grow plants down, or alongside.
If you do this now you will get quite a good barrier, by next year you won't be able to see them,
Don't be tempted to plant bamboo in the ground, you will regret it for years. that why you put any tank on bricks.
loads of amazing bamboos to choose from, make sure it fast growing clumping, and the thick stalks will absorb some of the noise. mix colours, and it really creates a brilliant screen.
If you know anyone with big clumps of bamboo, they are usually more than happy to let people dig big chunks out, most positively encourage it,with desperate smiles, pay someone to do the digging bit(hellish)
out of all the trampolining screening methods I have experimented with, this has had the most satisfactory results.