Strange engine noise please help!!

[BlackGT05]

If anyone has any thoughts they can give me great... I have been noticing a strange sound from my engine. It occurs under hard acceleration when I shift to second and third and it also happens when I'm cruising along in third and step on the gas hard. It sounds sort of like a hiss and knock sound mixed together like the engine is about to stall or something. It doesn't last long only a second or two...The car is stock except for mac axel-backs. My take is the variable cam is causing it or I have a bad fuel injector. Anyone else have this problem?

 

[boss377]

I'm seeing the same thing. And I think it started when I filled up w/ ethanol-blend. It's the concensus of several techs at our store, who are getting customers complaining about knocking and slight power loss during high engine loading. Hmmm.........