Here's an odd one. I calibrated my home theater to match speaker levels using the S&V disk. I then tested those levels using the THX optimizer on Toy Story II. Everything was spot on. I ran the internal test tones on my receiver(Denon AVR-1803) and my surround back speakers are about 5 db higher than the other speakers, which are all identical. It's quite a noticable difference. Everytime I run the internal test tones I feel like ducking because the back speakers sound so much louder than the other ones. Yet, source material on a dvd sounds like I expect it should. The surrounds never dominate and seem to be properly calibrated as the two calibration disks suggest. Any ideas on what would cause this? What's going on here?