I've seen (and heard) on occasion people clapping during Amidah, and I've always wondered why. Personally, I find it annoying, so I was wondering if there was some source that explained the reasoning behind this.
Rabbi Nachman of Breslov had a personal belief in the power of clapping, and put this information in Likutay Moharan. Those who count themselves among his students clap to tap into this power to this day. Here is some information about why they believe this.
It is worth adding that Eruvin 65A forbids distracting others during tefillah, and this is brought in the Shulchan Aruch as the halacha.