neXib

I've had a sound when I floor the car that I was afraid was a detonation sound, so I went to higher octane, but as it turns out, now it's even a lot colder outside, and the sound still came when I floored it onto the highway, and I managed to listen more closely to the sound, and it doesn't sound metallic. It sounds like some air/plastic sound, like a vibration, and it only comes sometimes over 8000rpm, maybe when I'm moving a little sideways at the same time. It's not just in high speed, only when the revs are high. I couldn't reproduce it when standing still and gear in neutral.

Could it be something with the intake? We took on and off a clamp on the intake tract when we changed oil (because the filter was on like hell, had to use different tools). However I'm a complete n00b so I wouldn't know if there's anything there we could have done wrong. Any ideas would be appreciated, it's no biggie, but an annoyance. I'm pretty sure it comes from upper engine bay area. But can't say 100% sure.