I cannot really make-out how the unit is zoned but it appears there's a zone damper on the return, just above the furnace? You did state it's installed as a down flow installation? A 33 code is a limit open. I'm guessing you have insufficient airflow on high fire. Prior to now, perhaps it's been warm enough that the unit operated on low fire only and so was not a problem. Now, if it's colder outdoors, it could be stepping up to high fire and tripping the limit. Again, this is pure guessing on my part, absent being on scene. Unfortunately you don't have a User Interface that is normally used with an Infinity product so there's no history of errors to help with the diagnosis.
The noise could be a multitude of different things and may or may not be related to the error code. Being from Massachusetts where we get our share of snow, we always install our units as sealed combustion installations. That is, a second pipe is installed to the outdoors for combustion air, thus eliminating the need for indoor air. This increases the overall efficiency by not using treated air for combustion and also is a safer installation in that the combustion products, absent a failed heat exchanger, are separated from the indoor environment. But that does cost a little more on the install.
Perhaps now that the long holiday weekend has expired, you've had more success locating the installing company? It seems unfortunate that you used a one man band for the installation. Those of us with companies of multiple trucks and personnel are always available. Keep us posted.