Can helicopter rotor produce infrasound?
Yes. Each rotor blade produces a pressure wave. Here's an example from a Chinook: 



At a rotor speed of 4 rotations per second, that's 12 pressure spikes per second, or a frequency of 12 Hz. At frequencies that low, you can hear the individual waves rather than a coherent tone (try this Youtube video on a good set of headphones). 

At high levels you tend to feel more than hear this frequency: you can feel the pressure variations on your skin, your eardrums and in your lungs, and you could get resonances in your body.