Yesterday Ed and I went around the pattern a couple of times. On our first departure there was a funny sound in the back, I turned to Ed to ask him what it was. We really had no clue, but presumed it was probably the tow bar and other baggage meeting in the back. Well after a couple of landings we went back to parking. When Ed was putting the covers over the rear window he pointed out we did not have an ELT antenna. We put 2 and 2 together and figured out the sound was the ELT antenna banging the tail as it fell back down to earth. Has anyone else heard of this happening, it seems to be a very flexible antenna and not something that would snap? Pretty strange?