Sucking noise/rattle whenever I accelerate hard at mid revs

[Neo]

I noticed yesterday suddenly that a noise is coming from the engine area every time I hit the accelerator while above ~3000 rpm. It tends to be more pronounced in second gear and happens in third and fourth, but not so much first or fifth.

The noise is like a short sucking noise at the moment I press the accelerator, like air being pushed out of or sucked into something, but it only happens if I accelerate hard while above about 3000 rpm. Sometimes, I hear a slight rattle as well. It's a little worrying (fortunately, I have a warranty), but does anyone have any idea what this could be?