Khoi:
I have no explanation for the lack of a power switch on the later Sidekicks, but I do have a fast, easy solution: Get an earlier Sidekick that does have the feature. I consider it essential, because if you attach a Sidekick while the hose is "live" and the brushroll starts turning, the brushroll can injure your hand if it happens to be in the wrong place.
So far as the noise is concerned, Lux PNs are noisy. They just ARE. I have Lux PNs that have been serviced, are all OEM parts, are in perfect adjustment - and they are still noisy. What's odd about that is that, before PNs, Luxes used to be famous for their well-bred, "hushed" sound in use, the perfect "maid's vacuum" that wouldn't disturb Milady while she was nursing a hangover.
PN-1s and PNs 5 and 6 are quieter than PNs 2 and 4, because of their plastic housings. But I still wouldn't call them quiet. And my Sidekick is the noisiest of them all.