I second using a night light. And unless I suspect a poop at night, I don't change the diaper. We bed share and my didn't wake up that age at night or make much noise, she would just bat at me when she needed to eat, so I don't have much to offer in that department. But unless the baby was awake, I don't think I'd respond.
It took me so long to figure this out! My DD was a very noisy sleeper sometimes. Generally, though, she would fuss if she wanted to eat, and I just assumed that was the only reason she'd be waking otherwise. So even though she was right next to me in bed for the first three weeks, and then moved to a crib in our room, I didn't get up unless she fussed, and then I just assumed she needed to nurse. Over time, the night noises reduced--by three months or so she wasn't such a noisy sleeper, and so if she cried out, I KNEW she needed something (generally, just eating--dirty diapers never seemed to bother her much).
So I guess my advice is, maybe wait to see if he actually seems upset or needy, and otherwise try to assume it's a sleep noise? If he really was hungry or needed a diaper change, I'm guessing he'd probably do more than just grunt or squeal. If he's just kind of talking a little, you might be surprised by him falling back to sleep on his own (my DD often did).
If DD needs to eat or is otherwise uncomfortable, she won't stop with the noises. She rarely cries out but she smacks her lips when she wants to eat or rustles around continuously in her bed until I get her up. Also, we have this turtle nightlight that puts the constellations on the ceiling and that is just enough light for me to see what I need to without disturbing us or DH.