The creaking may be the six bolts holding the large reinforcing plate under the engine - those suckers need to be really tight otherwise the whole plate creaks etc.

These bolts have been endlessly debated here, as BMW state they should never be re-used but replaced - single use hardware. I'm not going to comment on that aspect one way or the other (step away from the fuse...!) but I have heard that if they aren't tight enough, the reinforcing plate (or the bolts) creaks like mad.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)