Tetra Tec Ex700 Annoying Noise

[cambojnr]

So I got my new fluval 125 aquarium 2 days ago after my old 60l exploded, and I said that if I ever set up a new tank I was gonna get a good external as dont like the look of internals like the fluval U2 I have with I think is broke most of the time cause its as quiet as a flys fart. anyways got the ex700 today, set it up as per manual said so and its making an annoying noise, its not air as shook it around alot and no more is comeing out, also took it apart and reasembled it and made was still makeing the same noise. only other thing it says is put vaseline on the O rings but dont have any and dont see how it qould make that much of a diffrence, any ideas? thanks