After having this issue with one of my speakers, trying everything and being completely stumped - I went online and found a bunch of fixes but none which mentioned the D2 speakers.

https://www.fixya.com/support/t8352847-one_m_audio_bx5

Figuring there wasn’t much left to lose if it doesn’t work, and sugar coating it to myself by saying it’s an excuse to upgrade - figured I’d give it a shot.

Taking a look inside the case showed at least one blown capacitor (pic coming soon) which seemed to be the issue.

Replacing both of them with the following spec capacitors did the trick:

4700uf - 35v (https://www.ebay.co.uk/itm/264484014866)

At first it seemed kind of impossible with the glue / hard resin keeping them in place - but if you give them a tug from side to side they will crack the resin and come out of place a lot easier than you think.

Disclaimer: I’m not an electrician, barely a hobbyist - this may work but be safe about it.