As Bill stated the flue gas, from the furnace, is condensing and dripping back down the flue and leaking out at the connections. It looks like it may be due to an over sized flue. With regards to the indoor blower starting,stopping and then restarting - this is not a good situation especially if the outside condensing unit is doing the same thing. It's not good for electric motors to bang on and off. There is no way someone can troubleshoot this problem without actually looking at your system and testing the electrical circuitry. Let us know what the tech finds.