It's a pretty neat and inexpensive idea and who knows, it might even work. Having said that in my 'real' ultrasonic cleaner, I have found that using a good degreaser formulated for use in ultrasonic machines is key...after trying all sorts of cleaners that were supposed to work, I found there was nothing like the 'real thing'...I'm using an Omegasonics product; it's expensive, but it works extremely well and from now on I will not waste my time or money on anything else.
real deal cleaners are great , some can have a pain in the arse noise. were not supposed to hear that freq .maybe its the parts setting up reso freq.?
these zenith 1s are top notch , ya cant go past them.....till you see the price , always borrow time with 1 , buying 1 will send you broke. http://www.zenith-ultrasonics.com
on the tech theres info on freq . dont know if it mentions .... you cant leave stuff in some of these things cause they can eat holes in aluminium but I think thats for the cheapo market.