Volca Keys triggering unwanted additional note

[Temperary]

I've had my Keys for a long time now but this problem only started recently. It started when I was sequencing it via MIDI with an iPad app called Fugue Machine. As the sequence I was programming played I noticed that there was a low note playing that was not part of the sequence every time any note was triggered. I stopped the sequencer and played a few notes on the touch keyboard. That was also triggering the same low note in addition to whichever note I played on the keyboard. When I turn it off and on again the issue stops for a little while but then comes back as I play it.

Has anyone else had this issue? It seems like a possible firmware issue but I can't seem to find a firmware update for the Keys. Could it possibly be caused by the iPad sequencer? The midi interface I'm using is pretty cheap and might be sending some kind of noisy signal. Though since the problem also appeared on the hardware itself I'm not sure.

[Koekepan]

You may have a stuck note situation in its firmware.

Try putting it in poly mode and playing three notes concurrently?

[MeneerJansen]

I do not think it's a firmware issue. I do not have this problem. There might not even be firmware on the machine to upgrade (might be all ROM, no RAM). The stuck note explanation seems the most plausible to me. Have you tried changing batteries? Because some devices behave very quirky when the batteries are low. My flanger starts to output a high pitched tone for instance.