HI JOdi,
My lo would sometimes grunt out of fustration but lots of times I think that it was that she had just figured out how to make that noise and it amused her. Just wait til your lo learns how to scream. Tatiana was about 5 months old and she would screech away. I thought that she learnt it from a sreamer at the daycare, but my friends lo did it too and he doesn't go to daycare.
As for the teething I thought that Tat was teething around the same time frame but no teeth until 10 months, I think that chewing on stuff is natural and the drooling started around that time to.
your lo may be taking longer to get to sleep b/c he is learning that he can fight it now, just try to be persistant with your routine and he will figure out what's going on.
Good luck