Could be a combination of things,
How's the track and balance in the turn? Is it worse one way or the other?
How steep a turn are we talking? eg would there be an increase of g's and therefore an increase in the effective load felt by the machine?
What sort of line are you using? Length? Is the load spinning?
Not having a go but does this just happen to you or are the others who fly it experiencing the same problem? Has it been happening for a while or has it come on suddenly?
Sorry for all the questions but I'm sure it will help someone come up with a solution for you.
Any extra bounce could very easily turn into collective bounce with the collective friction a little loose or as others have said the transmission dampeners on the way out.
I have had collective bounce a couple of times in different machines and each time it was induced by my being either too stiff on the collective or a bit rough on the controls.