Hello, and welcome to the forum

I think it was definitely Rick shouting, and I, like you, think that has to mean he's successfully directed the herd away from Alexandria. It's really interesting what you say about Glenn, but I think Glenn and the others were a good distance away from where Rick was, so I'm not sure if it'll be him or not.

Something's definitely gone down though cos Rick was defo sounding panicked!

 

Its a good theory but the promos don't really match it. One of the promos shows what is happening elsewhere at the moment that Rick yells to open the gate. It shows Deanna overhearing Michonne explain to Maggie that they had to leave Glenn behind. She also says that Glenn told her he would give them a sign if he was ok. Right as Maggie lowers her head to cry Rick yells open the gate and everyone looks in that direction. It would be weird, "hey Maggie your husband got left behind WAIT here he is, nevermind." Also another promo this coming episode shows Maggie gearing up to go somewhere and I think its pretty apparent she is going to look for Glenn. I also don't know why Michonne would tell Maggie that Glenn said he would give them a sign unless something is going to happen later making them think its Glenn's signal... whether it actually is or not.

But Rick's voice does sound urgent and I don't see him leading the herd to the gates so I think it is very plausible that someone is injured. If Rick got the RV started then his plan was to loop it back and meet up with Daryl, Abe, and Sasha to continue leading the entire herd away. Assuming he did that then I'm thinking he's got Abe and Sasha in the RV and Daryl is elsewhere because we all know they aren't going to make Daryl ditch his bike. Other promo material for later episodes imply that Daryl gets captured by somebody so this is a logical place for them to be separated. Sooooo I think Abe or Sasha is hurt but I doubt either is bit.

 

It was definitely Rick shouting to open the gate. I saw several comments from people mentioning that with subtitles on, that part reads "Rick: Open the gate! Open the gate!" I didn't watch it with subtitles the first time, but I later rewatched the episode and turned them on for that part, and it does indeed say that it's Rick saying this. So that's one mystery solved. Unless this is some expert level trolling on the part of the producers lol