There is heavy dust build on the woofer baffle area-needs a good cleaning.
This should be done every 6mths (panel discharged.)
The only way is to use the small head on the vacuum cleaner https://ibb.co/RYs0tkQ and go over it slowly up and down and on the panel. Put some soft tape on the head so you don’t scratch the panels black paint.
If you have stuck on greasy dust, then the only way is to remove and wash the panel, can be risky though, but if you search you’ll find they do it.
Cheers George