Hello fleamrk,

Several possiblities here. Not static sound means the plasma discharge plates aren't energized.

1) Missing, cracked or defective discharge plate (you say you cleaned the filter - did you mean the lint screen in back, or the glass or white ceramic plate inside)? No plate, no ozone (O3) production.

2) Bad connection in the high voltage leads*.

3) Bad electrical components*.

*I'm not an electrician, and recommend that only qualified personnel troubleshoot high voltage electronic, both for safety, and for preventing further damage to circuitry. Visible problems, such as corroded or broken terminals that can be swapped when it's de-energized (unplugged) is one thing; having to dig deeper into the electronics is something that I expect to rapidly end up costing more than it's worth.