I'm glad you visiting students know not to talk
We had parents in one of my classes that would nootttt shut up, and then some visiting student finally told them to be quiet because even they couldn't hear. It was great. We all thank you for your respect!
FYI: this happened today, where a student wanted to sit in on a class but missed it/couldn't find it etc. She, by herself, approached my teacher and asked him if she could sit in, and he was very chill about it (no one really shows up to this class on Fridays anyways). So, look on the COD ahead of time, and if you're interested in a few classes, don't be scared to go and ask. There are a lot of "main buildings" where tons of classes are held, so for the most part, classes aren't hard to find. Also, if it's a smaller class, you could always email the teacher ahead of time and ask, it's really not a big deal. If they have a problem, they'll politely decline, but I'd be surprised if most aren't totally open for it unless there's a capacity max.