Mamiya 50mm RB Sekor C Lens making a Clunking Sound

Hi everyone,
I suppose I have some explaining to do with a Bronica645 User Name...
I recently purchased a Mamiya RB SD outfit although separately from all over the place.
I just received the 50mm RB Sekor C Lens, although I haven't received the Mamiya RB SD Body as yet.
There is a noticeable clunking sound as some slight glass movement, just wondering if this is normal
as it might something to do with the floating element or is it a defect?
This lens has a silver collar on the rear of the lens, would it signify I will absolutely need the Mamiya Spacer Adapter
for use with the Mamiya RB SD? Your replies are greatly appreciated.

Hmm, that clunking sound doesn't seem right to me. I'm new to MF so I'll let others chime in on that, but I can't recall ever running across a 35mm lens that clunked and my two Mamiya Sekor KL lenses don't. As for the spacer ring, I've added a photo of my two lenses, the 90mm on the left has the spacer ring, the 127mm on the left doesn't. I don't think the ring is actually needed, IIRC it is just there as an assist when mounting the lens. But I could be wrong on that. Here is the photo I uploaded:

(there was a url link here which no longer exists)

Thanks for the reply, agreed, I have never owned a lens which made any kind of similar sound either.
The thing that is throwing me off is the floating element, since I never owned that type of lens.
The Mamiya Spacer in the photo seems to make quite a difference visually, if I could do without, great.
Thanks for the excellent photos to compare.
I should try the lens out at least then see about returning it, other than that, the lens was well taken care of.
Hopefully someone that actually owns or owned this lens will respond with a comparison.