Does boxing/unboxing occur when a method accepts an out/ref parameter of a ValueType?
For ref Keyword Its already mentioned on MSDN that :
Do not confuse the concept of passing by reference with the concept of reference types. The two concepts are not the same. A method parameter can be modified by ref regardless of whether it is a value type or a reference type. There is no boxing of a value type when it is passed by reference.
As for out keyword:
The out keyword causes arguments to be passed by reference. This is like the ref keyword, except that ref requires that the variable be initialized before it is passed.
来源：https://stackoverflow.com/questions/5103147/boxing-and-unboxing-when-using-out-and-ref-parameters