Rattling rear wheel concern

[billium]

My Whyte E160 has always had a bit of a rattle at lower speeds on bumpy trails and I have not given it much thought but today I decided to pin it down and found out that it is the rear wheel!

With the wheel removed, if I just grab the top of the tire and shake it up and down I hear the sealant sloshing around AND a metal-to-metal clunk.
There is no bearing play and everything works fine so is this normal movement of freehub dogs or is something wrong?

The attached 3 second video demonstrates the issue.

 

[billium]

I think I found the issue.
The cassette felt tight with no wobble but it had radial play so the sound was likely parts of the cassette stack slamming into the spline of the freehub.
The lockring was tight - but not tight enough ( certainly not 40 Nm).
I have cranked it down tight and the noise is much reduced but I still have some radial play so there is likely permanent damage.
So, which is more likely to be worn - the cassette, the freehub or both equally?
And, is there any bodge I can do to fill the slop between cassette & spline- e.g Loctite Red or epoxy or teflon tape perhaps?