Being in the business, I can certainly notice the changes, and the different noises. A few years ago, when the first Airbus A320's started coming into SEA, noise complaints increased dramatically. It didnt help that this was about the same time that the third runway opened, so people were blaming the increased noise on increased traffic, not the ac.
As noted before, the approach to KSEA, due to airspace, has a very defined location for a drop from 9000 to 6000. Depending on the ac, (especially the 320) this is a huge noise generator...and the public took notice.
Having worked with the noise gathering data at SEA and PDX, the models used for the calculations leave quite a bit to be desired, basically leaving out noise reflective issues such as vegetation, prevailing winds, inversion/marine layers as well as aircraft type/configuration settings.