I had exactly the same issue with mine recently and managed to cure it. It's basically parts of the metal frame rubbing together. There are small pieces of felt stuck to parts of the frame to stop this happening and on mine some had come adrift. I replaced the missing pieces with small strips of the self adhesive foam used to stop draughts around doors and window frames you can get in DIY stores!
The best thing to do is drop the hood down, manually unclip the rear cover and raise the hood halfway up by hand so you can see the hood frame mechanism. You will then be able to compare the passenger side which you say is ok to see where the felt pads are. Before doing this, I also managed to see where it was rubbing by lifting the flap which covers the hood frame with the hood up and pushing the frame up and down with my fingers.
I've had the hood up and down a few times since and it still all seems fine.
I hope this helps as it was driving me mad too so I know what you are going through!