Suspension knock/rattle
 

I have a 2005 CRDi automatic, which has covered 65000 trouble free km's. I have an annoying knock from the front of the car, which is only heard when the car is under power. If I take power off and coast (in gear) the sound doesn't manifest itself. Even light acceleration displays the problem. I have checked the struts, all bushes and linkages and the brake assemblies. I have also checked the engine mounts and all cables etc. to see if they are touching somewhere as the motor "rocks" when power is applied. I also checked the drive shaft to the rear wheels, but all seems OK. The sound is a dull knock, that is more or less in synch with road bunps, but not always. At times it sounds almost likea loud diesel rattle from the motor. The dealers have lubed and tightened the sub-frame mounts and checked the vehicle, but cannot find the problem. Any ideas out there? I want to change the 235/60/16 tyres for 215/65/16's to reduce unsprung mass. Any thoughts on this?

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