Kev,

First point - the rattly idle: this is perfectly normal for the LA and its predecessor, the FP. Many plain bearing engines do this. It's caused by endfloat of the crankshaft which manifests itself as a rattle at idle but clears up as the revs increase when the thrust of the prop pulls the crankshaft forward.

Second point: the fuel tank may need looking at. LAs tend to draw their fuel pretty well so I'd expect the problem exists in the tank or clunk. Perhaps the clunk is getting stuck on a roll to starboard.