The pilot reported that, during the descent to final, he began the GUMPS checklist. As he turned on the fuel tanks, he picked up interference on the radios. After fixing the radio situation, he continued the checklist. During the landing flare, he noticed that the "runway sight picture" seemed lower than normal. As he noticed this, he looked at the landing gear indicator, and the landing gear warning horn simultaneously sounded, so he initiated a go-around. While climbing to traffic pattern altitude, he noticed that he had failed to extend the landing gear. He added that he had not heard or felt the airplane contact the runway before the go-around. The pilot subsequently landed without incident and noted no damage during a cursory postflight inspection. He then departed and landed at another airport. Subsequently, he performed a more thorough postflight inspection of the airplane, during which he noticed that the marker beacon antenna was shaved off and that the lower fuselage of the airplane had sustained substantial damage consistent with ground contact.