I'm having problems with my Mission Centre speaker. When I play a dvd through my system the speaker is nice and clear but when I have sky on through the system (av receiver) the dialogue on some channels is very distorted. This is also the same when I listen to radio channels through Sky via an optical cable. I have taken the speaker back to the shop but they saythe speaker is fine. The problem seems to have occurred when my son turned the volume up very loud when the av was off. I then came to switch it on and it was very loud for about a second then it shut itself off. Any ideas?