PS3 / Onkyo 605 HDMI Question

[Croweyes1121]

Hey, guys. I just got an Onkyo 605 and I'm curious about something. I just noticed that when I have my PS3 on and no movie or audio playing (just the XMB onscreen), that when I crank the volume up extremely loud, I get a kind of low, reverberating sound from my speakers. It's kind of a "hey, you're cranking this up really loud, be careful" kind of sound. lol It's not at all audible at standard listening levels (only at up over 85 volume or so), so it's not a huge deal, but I'm wondering if this is normal. The sound goes away when I turn off the PS3, so it's obviously either some signal the PS3 is sending to the receiver (could the video stream information be bleeding over into the audio somehow at an extremely low register?) or some degradation in the HDMI cable, but I doubt the latter because it's a brand new cable. Any ideas on what this is? Is it normal?