PAiA overtone problem

[myrr...@gmail.com]

Hello to the Theremin Nine~~

My Theremax has developed a second tone in addition to the first. In
the middle registers (don't know the Hz, but it's around A-440) I'm
hearing an overtone that's a diminished-fifth lower, and it's really
annoying.

Anyone else have a Theremax? Anyone else have this problem? Anyone
else fix it? (Don't send me to the PAiA website, it's all electronic
Greek to me.)

Thanks for any help in advance....