Repeatedly showing up to grand rounds as a visitor and asking questions from the back is just plain weird, period. I don't know where you heard that from, but please... don't do that. That's not a thing. And depending on what department it is, it may not be open to visitors. Grand rounds, even if open to the public, aren't intended for visitors to show up and ask questions to impress the faculty, or for visitors to sit in the back hoping to get noticed as a potential future member of the department. They are didactic sessions for residents, faculty, and sometimes other staff. More likely is that you'll end up sitting in the back and go unnoticed (if it's large enough), or just look like a weirdo if the grand rounds are smaller (like in smaller subspecialty departments). If someone tried this repeatedly in the departments I've worked in, they would annoy people and come off as a creepy stalker of the grand rounds.
