USB shielding

[Kitwn]

You've found it, that's the point.
You could try a ferrite sleeve round the mains lead to the PC. Cheap and simple to fit. Something like this...

https://uk.rs-online.com/web/p/ferri...2489/?sra=pstk

RS have a range of sizes. Look for one that's a close fit on your mains lead.

Kit

[Voicecoil]

......or even on the mains lead for the extractor, as close to it as possible. Often with EMI issues, prevention is better than cure: if you can stop it radiating, then you don't need to shield from it. Does the motor in your extractor make quite a howling noise? If so it'll be a high speed series wound motor and the interference is likely from sparking on the brushes. There are suppressor modules (resistor + cap) around that normally ought to be fitted on a quality motor of that type.