RNS-E fan noise

[TaPaKaH]

In recent weeks, the RNS-E unit inside my car has started producing what seems to be fan noise.
It takes at least ~3000 rpm engine noise or ~120 kph wind noise for the RNS-E noise to fade in the background.
The RNS-E noise always appears after 10-15 minutes of driving irrespective of RNS-E being on or off and takes at least 5 minutes of turned off ignition or a pulled Radio fuse (#39) to go away.
The RNS-E itself remains perfectly functional (even throughout 6+ hour drives with sat-nav) and remains cold to the touch.
The only configuration change to the car in the last 3 months was a winter/summer tire swap.
The only potentially related issue is (what seems to be) an excessive amount of window fogging inside the cabin, which indicates a high humidity that might affect the RNS-E.

I am wondering if anyone else has encountered or read about this or any similar issue?
Is it just a case of just a bad fan (i.e. bearing kaput) or can the default fan actually produce such a level of noise? (say, if RNS-E detects overheating)
Could there be some thermal paste inside the RNS-E that has gone bad and might be in need of replacement, or a temperature probe being dead or covered by dust?

(I don't mind taking the RNS-E apart in case it's necessary and, before you suggest, replacing RNS-E with an aftermarket system is a no-no for me for car's originality's sake)

[QuRace]

Subscribed.

While in my case, the noise level itself is not the problem (it's quite faint and only noticeable w/ the engine off), my RNS-E fan is on ALMOST ALL OF THE TIME (IIRC), even with no DVD in the slot. Was more thinking along the lines of air flow restrictions due to dust buildup over the years, but have no hard facts whatsoever ATM.

Thus, looking forward to your detailed-with-pictures thread of removing, opening & inspecting/cleaning the unit.

.

[TaPaKaH]

Just realised that I didn't report back on this.

So I disassembled the RNS and found what looked like remains of a CD label that shredded from spinning and were all over the drive bay. There was no dust whatsoever. After vacuuming the internals and putting it back together the RNS has been working perfectly (and quietly) for months already. So it was either the cleanup or inevitable cable connector wiggling during (dis)assembly that got my issue solved.

Note 1: Do not get RNS removal keys from AliExpress. Ordered two sets from different sellers and got ones that did not work. Ended up getting correct ones on eBay from Lithuania.
Note 2: RNS is a pain to take apart. Some screw sit too tight and using PH00, PH0, PH1, PH2, PZ00, PZ0, PZ1 or PZ2 only messes up their head, so the only way to get them out was drilling.