I was talking to a local last night 12/12/2016 and at about 20:30 an echo started to appear on our signals, at one point it was so strong I had to use semi break-in because I couldn't hear what I was sending. The return echo was about the space of a dit at 22WPM, so if I sent a dit, I would dit a dit returned, so it sounded like I'd sent two dits. As I say, at one point is was so strong it was as loud as the sidetone monitor, so I had to switch from full break-in to semi break-in. We were located about 11 miles apart and sometimes the echo was on both our signals then it faded and appeared on only one of our signals, which is strange seeing as we are only a few miles apart. This all lasted for about 10 minutes. The return echo was quite fluttery. Conditions on 80M last night were terrible. I've got no idea what this is, so I'm wondering if anyone else might have a theory?