Pad sound issue


New member
Hi all. Brand new here.
Just bought a second hand RockJam Dd502j kit, and everything works great apart from when I am plugged into the amp, the 3rd Tom (floor Tom) sounds like it's really quiet, and far away. Not as crisp and loud as the others. I tried adjusting the volume and nothing changes.
The bizarre thing is though, when I unplug from the amp, and change to headphones, whether it's directly into the module, or through the amp, the KICK pad has the same sound issue, and the floor Tom is fine!
I've messaged the seller and they have NO idea why it's doing it.

If anyone knows what is going on, I'd love some help.

Thanks in advance.