Tube Problem

Sorry if this is not the RightThread

i just bought the avantone cv12 used and works just fine.

after 3 month i start to hear click sound even when the power is off

i still Hear click sound coming from the mic.

i don't know if is it the tube need to replace or the cable 7 pin xlr need to replace i don't know this is my first tube mic

Also How Do i Know if the tube need to change does it the color of the tube change turn into black or something ele's