I just got a Yamaha Rx-v520 (like the Htr-5450?). This is my setup: 2 speakers for stereo, a sub, a sub amp, and the Yamaha. For some reason when I turn on the "effect" button I get humming from my mains (the receiver doesn't hum, just the mains) even at the lowest volume setting. When I leave the effect button off everything is great. Also, when I press the "effect" button there is a loud pop like the Yamaha just sent my speakers a jolt! I don't know if this is because I only have the mains connected? Has anyone experienced this problem or is this normal for a 2channel setup? I also own a HK320 and used to own other entry level receivers and this is the first time I've encountered this.