I think it's pretty quite. I have heard some others and this is much more quite. It's not as quite as an EU, but it's mucho cheaper. The muffler is about a foot long and oval on the end, about 6x9. Like a very, very small car muffler. The exhaust opening is maybe 1". I was thinking about putting some sort of car muffler setup before it showed up, but now that it's here I won't bother. I think I might try a pipe with a 90 going straight up for 4-5 feet. For the mechanical noise, I will try a four sided box made out of 4x8 plywood with carpet stapled to the inside to absorb some noise. Top would be open.
The original link died with the $150 off deal, so I put a link to the regular price. If you are interested, keep checking costco.com. It might go on sale again. Remember, Costco's regular return policy aplies. If you have a problem with it, you can return it to the store and get a refund.
Just checked, looks like they are having a special on the inverter models.
Look what else they have that I need to save up for.