2005 Ford Focus light knocking when wet.. suspension ,

When driving along an uneven road at slow speeds 15mph, I get a light knocking noise from the passenger side wheel area, "Usually when wet" virtually nothing when dry. Garage changed anti roll bar bushes, top mounts and drop links. The noise has a kind of hollow tone or knock. checked in wheel arch/engine area for any loose plastic knocking around. The noise can be heard going over speed bumps slowly as well, but most anoying is its rattly/knock effect when driving on slightly uneven road surfaces...nothing on a level road. Engine mount (gearbox side) checked as was all componants underneath and all seemed to be tight and no sounds from them, brake bads are ok too as noise is still there when applying brakes... but sound as if there is something really loose under there somewhere.