strange assomption i'd say. Rail system tend to be very customisable (that's why they exist) and I don't see why it should be the same for two different rifles.
I assume you talk about those holes we see on the left side. Is that correct? If so, there is in this model the exact same number that we can count on the picture on colt's website.
As for the sound and tapping, I think it's pretty cool (eventhough it's a little loud... or maybe not) and as someone already mentionned, there really no way to tell how it's going to sound. Just as an exemple, out of 50 Lee Enfield No. 4 modified to be unoperable (use for drill practices), none sound alike when you tap the mag like that.
True, it might be dumb to assume that it's the same for the M16A4, which is a totally different rifle, but imo it makes more sense than expecting that all rifles will sound alike when you do that.
I can't remember who put up that argument that the tapping sound was wrong... go back through the pages from this thread (or do a search in the thread). It was discussed back then.
EDIT: ... just did the search I suggested to you... nevermind that! It was you who brought the issue up back then. I guess you have already read the replies then... didn't you?