I've also been to every home game since around 1999/2000, and I totally disagree. The crowd was super loud yesterday, but there are a few reasons I think people mistakenly thought it was "quieter than usual":
1) The Jets weren't on offense very much, and when they were, the drives weren't long enough to sustain intensity. A lot of 3-and-outs and plays that didn't last long for the Jets offense. But whenever their QBs were under center, the Clink was rockin!!
2) Fans misjudge crowd volume based on what they hear on TV. The TV broadcasts use heavy filtering during the audio mix to reduce crowd noise so that you can hear the analysts. You can't judge crowd noise by the TV broadcast.
3) Fans in the end zone areas mistakenly assume that the volume they hear is the same as on the field. This is not the case at all. The parabolic design of the cover means that noise is amplified and directed toward the field, and reduces dramatically at each end zone. By the time you get up into the seating area, you are looking at a 40-50db reduction (and that drops exponentially as you move up in the seating areas).
4) Season ticket holders and fans who attend regularly compare the volume to games previously attended. But your brain has no way of accurately recording historical sensory data such as sound. It is impossible to compare without a decibel meter.
I was in CLB46, and every person in our group commented that it was one of the louder games this season. It was loud enough and wild enough in the Clink to rattle the windows in our suite, which is at the very end of the North end zone area (so no advantage of being under the cover where noise is amplified).
I've heard these complaints about volume a few times, but don't agree with them. I think it's due more to fans inflating their previous experiences in memory, which is quite common. That's what our brains do. When we think back to experiences we enjoy, our brains will always exaggerate certain elements of our memories. As I said previously, you have no objective way to compare sound without a decibel meter.
It'd be interesting though if someone had a decibel meter, and could go to games every week and record various readings so we could look at them later. Maybe I should buy one and do that. My inner science nerd just perked up at the thought of that.