Hello Everyone!
I am also experiencing the same problem with my Monty 2009 GLS SE 4x4 i.e. buzzing or humming low pitch, air whirlwind sound at low rpm (1500 to 1800) usually at second gear.. My good friend, a veteran buy and sell, told me it's common in Monty specially 4x4 variant, and nothing to worry about. He also told me that the sound is being caused by the nozzle of air intake pipe touching or vibrating against the plastic shroud around the radiator fan.. You can see that this design of intake pipe is really playing and not fixed.. Anyway at first I was adamant. But the noise is really annoying so again, I'm back at searching again the net for answers, until I found this thread.. Then I chance to found a mitsubishi forum with the same problem, although Outlander with diesel engine and realized that what my friend was telling me might be true afterall! Check the link and see for your self.. Also check the german post inside the thread (use translation feature of google chrome) and you can see how to do it as it has provided some useful pics.
Vibration / Buzzing Noise - Mitsubishi Forum - Mitsubishi Enthusiast Forums
Outlander im Alltag - Self-Made - Luftfilteranlage 2.2 DI-D dr
I don't know about you but I will surely try this first thing in the morning tom.. I'll post here my findings after.