I have a problem in cooling season with weak airflow to the upper level of a three level townhouse. The temperature differential between 1st and 3rd floors is 10-12 degrees. The design of the duct system is a flat main duct between 1st and 2nd levels. It has round branch ducts branching off to the registers. On the 1st and 2nd levels each register has its own duct run. Going up to the 3rd level it seems like several registers are combined on the same duct runs. The airflow is very weak and the only way to get the 3rd level reasonably comfortable is to run the bathroom exhaust fans to pull out some of the humidity and heat in the early evening. I have tried register fans and they dont lower the temp and only make a lot of noise instead. I have thought about adding a second system and ductwork in the attic for the third level. Before I seriously consider this, are there any other suggestions on how to improve this situation? Thanks!

Last year had some renovations done and this included having some new duct work installed along with a high efficiency furnace. In one area there is a vertical round ductline at an outside wall that is makes a ticking noise. My guess is thermal expansion of the duct somewhere. The location of the ticking effects the living room and our master bedroom and its driving me crazy. Is there anything I can do to try and remedy this before tearing into the wall. It's about a 12 foot vertical run, I have access below (in the basement) and it terminated at the register on the second floor. Many thanks, Detox