Recently, I hear very slight clicking sounds when driving my X, very slight and not all the time, especially when I press the gas and release it, the clicking sound appears. I put my car to dealer for inspection, they told me that the sound came from my transfer box, but it is very slight and can be ignored for the time being. Anyone here has the same experience? What could happen if I ignore it?

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--2004 E53 X5 4.8is - ECE version; right hand drive; Located in Hong Kong; ext. black sapphire metallic; int. leather black; adaptive dynamic bi-xenon headlights; 16:9 onboard monitor w/o navigation; 20" genuine BMW Y-spoke 214 wheels with Bridgestone Dueler H/P Sport tires; Int. rear view mirror w/ compass.