2004 Renault Laguna 1.9 DCi Tourer Vibration through the pe

This is a problem that really has me stumped! The car has a high-frequency engine vibration that is felt through the steering wheel & pedals. It feels as though the engine mountings have been compromised, although an inspection of these has been made and nothing apparent has been found. The usual culprit of the exhaust heat-shield has also been checked and nothing can be found touching the exhaust system or steering rack. The car has recently had a new timing belt fitted by a specialist and the problem seems to be more noticable since this was done. The stabiliser & engine-mount adjacent to the timing belt housing have been inspected and found to be ok. Does anyone know if there is a balance shaft on the engine that could be mis-timed without upsetting the diesel injection timing?