I tried encapsulating the ferrite rod transformer using aluminum foil but the outcome was pathetic. Instead of improving the reception, I got very poor signal. So, my conclusion is that the ferrite rod is not working as a transformer here, but it's working like a supporting loop antenna along with the main loop. that's why covering the ferrite loop stick reduces signal. BTW, there is no point of caring about signal interferences because even if I use a toroid or won't use anything at all, the main loop will still pick up the noise. So, keeping the ferrite loop stick along with the main loop would only improve the signal strength.