I think its a matter of personal judgement. I do think its inappropriate to ask questions or make comments in the class if you have not been explicitly encouraged to do so. If you're not sure, I would definitely err on the side of not participating. As people have correctly addressed in earlier posts, the students have spent a lot of money to learn from these courses. If there's a class visit every week, and there are questions from visitors every week, it will be very annoying for these students and might ruin the learning experience.
On my Berkeley visit, I met an applicant who was quite obnoxious. We went to separate class visits, and I briefly asked him how his went and he said. "I think class visits are so bloody useless. I raised my hand and asked some questions and then I just got up and left halfway because I was getting bored". I could not believe what I was hearing. I really hope I don't meet him again!
I did speak during class on my visit, but I feel my situation was very different. I had a relationship with the Professor and he explicitly asked me to present something at the start of the class.
Unless you are encouraged to speak, I really wouldn't recommend active participation in the classroom.