No, you are not a freak, and not even unusual. I am a rather quiet cummer myself, but I have had my share of partners (men, I'm gay) that do all sorts of things when they cum. Screams, grunts, and spasms are not unusual. Spasm sometimes last long after. I've had other guys that develop a hypersensitivity in their whole bodies for a while afterward-- if you touch them anywhere in a sensual way they break out into shivers and spasms. One interesting behavior is to break out into uncontrollable laughter when cumming, and to continue for a while. The first time this happened, the guy was apologetic about it, and I thought it was weird. But since then, I've met a lot of guys that do this.
An orgasm is a very powerful event, so it's perfectly understandable that unusual and uncontrollable behavior may result. Personally, I find it very gratifying when my partner gets off in a loud or physical way, because I know I've satisfied him.