I know two people with Chicago Air compressors - one has only recently bought his, but the other has owned his one through around 6 years of service. I've seen both in action and they are impressively quiet, far quieter than any belt driven compressor I've ever seen. I'm also referring to the 50l 2 x 1.1hp models, not the smaller single motor units.
The long term owner, has rarely turned it off and it's still very quiet to this day. It's been used for lots of blow down, inflating and air tool usage and has even survived a long continuous run when a fitting failed while he was away for the day (and the unit was venting free air for hours).
If having to shift it around the shop is an issue, then because of the ally tank, they're light too.
Admittedly, some of the fittings have a look of being a little chintzy, but they are all generic parts that can be obtained either through SydneyTools or on eBay.
My local phone shop has also recently opened a branch with two units each with 3 x 1.1hp motors on them. Overkill for what I imagine their uses to require, but you never hear them run.