Best cheap way is buy some poly bushes for the dogbone mount (the one under the engine) and do this:
Undo the 4 big bolts bolting down the o/s mount.
Get a lever bar between the mount and the suspension turret (go carefull not to damage you air con pipes)
give it a bloody good heave, and the mount will slide forward - it will move a good inch, so you will need to adjust a bit, and try it.
what this does is move the engine forward, which in turn moves the exhaust manifold away from the subframe (which is the knocking you here)
dont forget to do the bolts up!