Hi Jeferson,

I've been having the same problem with one of my KT's as you have. One of them works great, the other one does not (and just like yours, it makes a noise like a Hornet's nest no matter how much you try to adjust the trim...!)
I have tested both of them using either transmitter and the same battery (with a low charge this time, but they have behaved the same way with a fully charged battery also) without seeing any differences in how they operated, so I have to agree with your original post - the receiver board is bad! [:@]

As The Blitz points out, the Heng Long "Smoke and Sound" electronics are much more reliable (or atleast consistant...?!), and easy to install. Wiring diagrams and instructions can be found here:
http://www.rcuniverse.com/forum/m_5760954/tm.htm

Hope this helps,
Mart