If you're simply looking to raise the ambient humidity, have you considered modifying a personal humidifier? A misting system would merely drench the entire substrate, wouldn't it? Well, I don't have any experience with misters so I dunno. Anyway I use an ultra sonic cool mist one, from Walgreens, for my Pyxie frog, with some obvious modifications:
Name: DSC_0941.jpg Views: 207 Size: 60.7 KB
I used to use the ReptiFogger myself, but then it started making these whining noises (just as yours did) that drove me nuts. And I fueled it with distilled water from day one, too. I was inspired to do this with an ultra sonic personal when I saw thread about somebody doing something very similar with the exact some unit as I have. It cost around the same (maybe less) as the ReptiFogger to make, but it runs much more quietly and, according to some, will last much longer. Even holds much more water at a time, up to 1.2 gallons.

As there's only one setting on the unit pictured, it puts out a BUNCH of mist, so I would suggest making sure Frog's cage is well ventilated (mine's a 24L x 18W x 12H exo terra, plenty of built-in ventilation there), and preferably rig it to a Hygrotherm. I've got mine programmed to keep my Pyxie's ambient humidity between 70 and 80%.