I'll weigh in on this from my perspective as a HERS inspector (I inspect homes for energy efficiency measures and a big part of that is the HVAC equipment). The noise peak with the Russia filter is possibly strain being put on the bearing(s) for the blower fan. If speed is dropping off by half that tells me that these things are jacking up the static pressure of the system (basically there is a larger pressure differential between the downstream and upstream sides of the fan) which will decrease the life span of the fan. The flat filter though definitely has an issue with surface area and thus you can't get really useful filtration out of that without also having static pressure issues. The ideal would be the Russian style but with a lower MERV media but something still good enough to reduce dust and other large particulate. The most ideal situation would be some heavy fabrication to create a filter box like you see in most modern vehicles where the filter slot is much larger cross sectional area than the rest of the ductwork but that would probably run into numerous packaging issues. Sucks to see this as I've been wanting a filter for my truck but for some reason never applied my professional knowledge to the situation. The crappy thing though is dust will also kill your fan over time so I'm not sure if the filter is actually possibly killing it slower.