This is a very interesting thread!
Working on these cars day in day out, as far as I'm concerned, all late model diesels have this noise - but some are quieter than others. In fact a friend of mine has just bought a Rover 75 Contempory SE CDTi Manual which has the noise, he was not aware of it until I pointed it out to him!
The problem lies with our old friend Project Drive, they did some plumbing to remove the secondary low presure fuel pump next to the battery, revised fuel pipes, revised conections to fuel cooler, etc. Ever since they did that, this noise is present. As far as I can detect where its coming from, it is caused by the PWM signal to the high pressure fuel regulator in the high pressure pump - this sets up a vibration down the fuel lines (you can best hear it with a stethoscope on the return pipe from the regulator. The alterations they made to the plumbing must have somehow taken out the damping effect within the fuel lines to set up this noise. I have swapped the Regulator from a good known early car and it does reduce the noise for a short period of time and then its back again....
So the 2004 facelift of Rover 75 / MG ZT started from VIN 321638, however, the fuel pump delete was from VIN 5D332301, so there are a few lucky facelift owners out there that "should" not have this problem!
The only solution I can think of (unless someone comes up with a fuel pipe damper - rather like the 75 diesel clutch pipe damper maybe!) is to fit the older type fuel system!
One thing I have learned from here reading all of this, is that MGR were aware of the problem and were in the course of dealing with it...
As for BMWs not have this problem, I wonder if thier engineers have a Project "FAHRT"!
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