How you are alerted to change the filter depends on how the control was configures at start-up. there are 2 types of filter, media (which is the solid filter thats been around forever) and EAC - electronic air cleaner (which works just like the electronic air cleaners you see in stores that have no filter). When the control is programed for use with a media type like the 4 inch filter you have the control will alert you when to change based on static pressure...for exaple you mentioned that your static pressure was at .45, the infinity system remembers that reading and will indicate the filter is 100% used around .76-.80 static. With an EAC the static pressure does not change so the control initiates a timer to tell you when to clean the filter.
just touching a few point about fan noise
1. variable speed blowers will be louder than traditional blowers due to the fact they will increas rpm to maintain airflow
2. short or hard metal return ducts will alow blower noise and noise from turbulent air to transmit into the home more effectivly and this noise can sometimes be aleviated by adding a boot (flexible transition or fiberglass ductboard transition) between the furnace and the duct to baffle this noise
3. in recent years contractors have oversized furnaces in relation to the condensing units to achieve better airflow for higher seer ratings and the tax credits which has resulted in installation where the heat airflow can be several hundred cfm more than cooling airflow and blower noise would be experienced in the heat mode but not cool mode.
the majority of the noise you hear from the blower is air turbulence and the duct system can either baffle this noise or enhance it. more rarely you might see excess noise from vibrations in the blower and if this is the case a soft transition to the main duct on both the return and supply as well as rubber buffers placed between the furnace and any hard surface would help greatly reduce that noise.
Twilly says get in touch with Mr Bill, Twilly thinks he worked on the design of that system.