Hygena APL2124 Extractor Fan - How to open?

[EwanWhoseArmy]

Hello, I've recently moved house and the extractor fan in the kitchen sounds like an aeroplane taking off when you switch it on. I've gone to the vent on the outside of the house and I can feel it kicking out air at a reasonable rate, so it seems to be doing its job, just it's incredibly loud.

So far I've got inside the hood and given the fan a bit of a clean, and now it's a little quieter on the lowest setting of 1, but still unbearably loud on the higher settings of 2 or 3. I would like to open it up further and give it a deep clean and maybe some WD-40, however I can't figure out how to get inside.

On the back there was a plastic cover in the centre that I removed which revealed a nut. I took off the nut, but then I'm not sure where to go beyond that. On the front there are two things that look like they could possibly be plastic covers for screws, but at the same time they don't seem to be removable. Please see attached photos, and let me know if there's a way of getting inside.

 

[EwanWhoseArmy]

I actually found a picture of the cover:and I seem to be right about the screw covers:
https://www.inter-spares.co.uk/hygena/hygena-extractor-fans-spare-parts/apm2325/blower-cover.html

However I still have no idea how to remove them, maybe the decades of grease have just made them hard to remove. Either way I'd be happy to hear if anyone has tips for removing screw covers like this.

 

[EwanWhoseArmy]

To add a conclusion to this thread - In the end to get the screw covers off, I drilled a small hole in the centre of each cover, then screwed in a screw which I could then use to pull it out. When replacing the screw covers later, I used a small bit of sealant to fill the holes. This allowed me to disassemble the case and give everything a proper clean.

Ultimately I think the cause of the loud noise while operating was that the fan blades were rubbing up against some part of the hood, so although cleaning didn't fix the problem, I think it was still good for maintenance because clearly the previous owners never replaced the grease filter in the extractor hood, and it helped me narrow down the real issue. While I had it disassembled anyway, I also added a bit of WD40 to the parts that move.

*Please note, I did all this with the power off. Ideally I could've just disconnected the extractor fan, but it wasn't going to be straightforward without disassembling the hood too, so I just had the power off during disassembly.