Denon 1910 - Sound drops for a split second every 20 mins or so

[MB1980]

Hi all,

Bought my Denon amp back in May. Everything has been perfect up until a couple of weeks ago, where the sound started dropping briefly every 20 mins or so.

This effects both the Popcorn Hour and PS3 I have attached, thats all I use.

Any suggestions welcome please.

Mark