That is the vacuum electrical box for the pods that is clicking. I have it also when its cold outside on my 260E (it'll click super fast for a couple mins then stop) -- I'm guessing replacement is only option.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k