I have an Insignia 5.1 surround sound system (http://tinyurl.com/7f8fzzl) and for the most part it's been great. When I'm watching cable, everything sounds perfect. BUT... for certain Blu-rays (not all of them, strangely, maybe 2/3 of the ones I own), I have to turn the volume up louder than usual in order to hear them (to 20-25, as opposed to 10-15 which is where it's usually set). Normally, this wouldn't be a problem... except that the center speaker emits a loud hum when the volume goes past 20 or so. Since the center speaker is where the dialogue comes out, it's very distracting. I've played with all the settings on the TV and Blu-ray player and Surround Sound receiver. Nothing seems to get rid of the hum. Any ideas?