CLP 430 fault with volume

[Openwood]

We bought a CLP 430 last year and I've noticed a fault:

When I play, the volume cycles through loud (and tinny sounding) to soft (and muffled sounding) regardless of how loud or soft I'm aiming to play. Fortunately, the instrument is under warranty and our local Yamaha-registered technician is coming to take a look at it next week but I would be interested to know; a) is this a common fault? and b) does anyone have some suggestions as to where the problem might lie?

Thanks,
James Henderson
Guernsey

[Lerakroxa]

Hi ,
I have clicked these pics , but these need some editing , can anyone help me with them please

Thanks for any help

Rgds
Atamvir