Since i bought my Yamaha DSP-A592 (Dolby Pro-Logic AV amp with 6-ch input), I've noticed a noise coming from the centre and surround speakers, which can be heard when the system is at low volume (and even when the source is not playing). The noise is similar to the hissing/buzzing noise which you'd hear when the speakers are turned to full volume without a source actually playing (the front Left and Right channels are fine). I've tried using different cables, and recently upgraded my speakers but it makes no difference. I'm using the 6-ch input from my dvd player now, but the noise just refuses to go away. I had taken it back to the shop that sold it to me, and they sent it away to be tested but they couldnt find any problems with it. Has anyone else had a similar problem, or know how to fix it?