Ask Abus if it's okay to wrap some rubber tape or add some plasti-dip coating to the shackle to dampen the noise.

They'll probably say any modifications void whatever warranty there might be. But I don't see how adding a bit of what's already on the shackle would hurt anything.

Or carry some rubber band mounts, the type used on many bike lights, and strap 'em around the junctions between the shackle and crossbar while you're riding. Should help dampen any vibration.