Silvery Sound Of Roman Denarii

Dear All, you know that a silver coin could be recognised by its perticular sound when dropped on the table. Obviously, fourrees do not sound like that because they have just a silver wash on them. I wonder, how often "normal" silver denarii of a period from Antoninus Pius to Elagabalus do not have this conspicuous silvery sound, producing instead something like a base metal coin? Are all such denarii - fourrees (and posibly fakes)? Best regards and many thanks for comments. Vlad