Well it seems to me that the lock ring isn't loosening but the sprockets do somehow get loose over the course of a ride and starts to sound quite noisy going over rough ground. What might the problem be? The Ksyrium Elite wheels and 105 cassette haven't had a lot of use but were fine for quite a while now I have to take the cassette off and put it back on after each ride – the lock ring doesn't seem to have loosened.

Is the freehub OK?

Well I think so – anything to look for?

Did you forget to put the spacer 105 cassettes come with back on the freehub before the sprockets?

(I've done that before…)

You are missing a washer from the cassette I reckon.

EDIT: wot tinklydave said.

no the washer is on. It's all nice and tight but loosens as the ride progresses – need about 100 miles before it's really loose; when I say loose the single sprockets move around.

If it's a10 speed 105 cassette you need to fit two spacers on Mavic hubs. The first thicker one comes with the wheel and is used for Shimano cassettes, and the thinner one is supplied with the 10 speed cassette.

Does the freehub also have another spacer?

(Seriously, some Mavic wheels have a spacer IN ADDITION to the extra 105 spacer!)

Is the lockring moving on it's thread?

(Edit: DAMN, now I'm too slow!)

Ah that must be it – I'll check; thanks.

If it's a Mavic, you have the spacer(s), then 100% it's your free ride hub that is on the way out.

Collected mine from the LBS 2 weeks ago for the same issue.

definitely a spacer issue

The mech' team at the 24hr solo champs thought it was a spacer issue too. As soon as I talked to a Mavic dealer they knew better and Lo, a new freeride hub was indeed required.

100% or your money back! 😉

I hope for the op's sake it is a spacer issue as he mentions the individual sprockets are loose. If the whole cassette wobbles as one unit then this would indicate freehub wear – probably wear on the inboard nylon bearing or worse the alloy axle.
Seems strange it's ok when first assembled though.

I had this issue with an XT hub. On closer inspection the freehub was hosed. I've also experienced the missing spacer issue with 10sp 105 cassettes but you know this is loose before you even set off, rather than working lose during a ride.

OK I checked and the thin spacer wasn't there so I put on another from a new cassette I have – I can only think the spacer wasn't there in the 1st place as it was on a bike though I did change the wheelset; really don't think I'd have put it back together without a spacer if there was one there. So I'll ride with it tomorrow and see how it goes.