I doubt a GI would carry an empty Garand clip just to throw it at hard surfaces, in the off chance it makes a noise remotely close to the ejection noise and confuses someone into revealing their location/breaking cover. That's one less clip full of ammunition you may need. I wouldn't say clips are 'rare' but they are certainly valuable to troops who want to store a few more rounds. Carrying what you can effectively must have always been a concern...and then you have the case of breaking the clip (something you also don't want to do).
Firefights are usually between more than just two people so this 'trick' would commonly be deemed redundant. There would probably be too many noises from other sources to focus on one particular sound, particularly at distances.
I'm sure its happened a handful of times in the most specific of scenarios, but it was probably far from common practice.
I'm sticking with the Carbine.
