EHX Stereo Polychorus I bought from a local dealer (I’m from Russia) doesn’t seem to be working right.

Whenever I turn it on and play a note on my guitar, the signal starts to self-oscillate the way it usually does when the FEEDBACK control is fully rotated clockwise. This noise emerges in any position of the knobs (even when all of them are rotated fully counter-clockwise) and in any of the four modes.

As the oscillation grows, the noise gets louder. It disappears when I change the mode to any other one, but emerges again when I play a note, touch the pedal (even when I touch the plastic knobs, not the metal parts) or move the pedal.

If I switch the pedal off, the same noise can be heard, but much quieter.

I’m absolutely sure there was no malfunction like spilling fluids on the pedal, frying it, throwing or making it fall from heights.
Nevertheless, I will be grateful for any advice.