I had to drop the turbo slightly to change the exhaust manifold and at the same time changed all the engine mounts recently. Afterwards I noticed that I was scraping the exhaust on speed bumps etc. and low and behold found it had dropped because of a worn out rubber centered metal exhaust mount tucked up awkwardly around the rear gear box mount. I fabricated a new nylon center from 36 mm bar and all now good. I suspect this mount takes a lot of wear, worth a check as I imagine it is easily forgotten.