If it happens at idle can you figure whereabout on the engine it is coming from? Internal? external? if you can take a short video of the sound with the hood up and post it to YouTube it would really help in diagnosing the issue.

I'm not sure what a "springy" sound is? I'm thinking of a cartoon-ish "Boing" which doesn't mesh with the rattle/tapping of lifters & rocker arms.

Process of elimination. Try to isolate it first and go from there. Give us updates!

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2007 E70 X5 4.8i Sport Package
8x,xxx Miles
"My Precious" (Smeagol voice)