Should audio be part of video or not? Like the videos of birds flying, cats playing, or boats faraway, the camera system would pick the background noise and unrelated chatter. Should the video be silent or still there needs be some sound bites? Please suggest what generally you do. Are videos without sound accepted by agencies?

I don't have sound on most of my clips.  Doesn't seem to deter buyers.  If the sound is high quality and the clip wouldn't be as good without it, I would keep it in but that's only occasionally for me.

Just about my thoughts as well. I have very few videos with sound in them. Some I do have sound because I think it adds value but out of 600 videos I'd say I have 20 with sound. I left in, for example, ocean waves crashing on some clips because there was nobody around to mess it up, I had my expensive microphone on my camera, and it was subtle, like one of those zen relaxation songs:)