Weird Engine Noise

My 09 will make a weird noise when heavily accelerating from a cruise at like 1500 rpm. Most of the time it happens when I get on it to pass someone on the highway. It is a "errrrch" kind of noise, kind of like a game show buzzer type thing. You can hear it above the exhaust. You can let off for a millisec and it goes away, then resume acceleration. Sounds almost like the engine torques over and a pulley grinds against something, but I don't see anyplace that looks like that is what is happening. Could it be the VCT? It used to do it even before I put the e-force on. Anyone have any ideas?

Its kind of too metallic sounding to be belt slip, I think. I don't see any black dust either. I am running a thumprrr tensioner too. I'll try and figure out how to record it on my phone and upload it. Its actually a scary sound, makes you lift instinctively as soon as you hear it. Otherwise she runs great though.