LHM, fast letdown can also cause gassiness, fussiness, burping, etc. If she's clicking I'd lean towards the letdown- all three of mine click and it's definitely not latch related, they do it when the flow is fast and heavy so they can let excess milk dribble out. They'd often finish and when I pick them up the lower side of their faces were all wet with milk they let go because they couldn't handle it all. Are you pumping purposely to save the milk? If not, and you're pumping before feedings, you're telling your body to keep making that same amount of milk that your baby can't handle - block feedings will suck for the first few days while you deal with engorgement, but is well worth it in the long run. I always have fast let down and I had oversupply with my first- nothing quite like a choking, angry baby every time you nurse who then screams for ages after because it's all wrong :/
Even if you do nothing differently, she WILL grow out of it. At some point the amount of milk you are currently producing will be sufficient, and she'll be more able to cope with the fast let down as she gets older and you'll have one of those miracle fast-feeders who chugs it down and then disappears to play when she's 10 months old or so.
Everett SCREAMS for about 5 minutes when he needs to poop. Nothing you do will help him, then he'll let go a big poop and everything will be great again. That's a first for me.
Grunting- this baby doesn't ever seem to need to burp. It's a little odd. I try to burp him after all our daytime feeding but he gets cranky when I move him to a burping position and never actually burps while I try. I don't bother at night any more. When he grunts it's because he needs to fart so he grunts and stretches and pedals his legs around and farts and farts and farts. So much gas, but he's not unhappy about it.
Casmer- I hear you on the fighting sleep. It takes a lot of very real effort to get Everett to nap. Yesterday he was wide awake except for one 20 minute nap in the wrap when we went to the park and then a 1 hour nap when we got home from the park and that was it. What the heck? The only way I can get him to nap is to swaddle him and rock/bounce/walk (all at once!) until he falls asleep, solidly asleep with his head lolling and his mouth wide open. Often he can look like he's sleeping but keep opening his eyes just a crack and if I try to put him down like that he'll be wide awake again in moments. He can be in that half-awake state for an hour or more and then suddenly POP- wide awake, done "napping" (nevermind that I've been holding and walking a 12 lb baby for the last hour, and now I need to hold him so he can bounce around and drape over my shoulder looking at things. Argh!) Recently I've been laying down with him and letting him nurse to sleep and then sneaking away. It is increasingly turning into the ONLY way to get him down, but it's going to be impossible to do when my husband goes back to work in a few weeks and I've got the other two kids to worry about.