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weird gpu fan behaviour

Level 7
I’ve been having a strange behaviour from my card’s fan, maybe someone here can help me understand and fix it?

The fan of that card is blowing faster than needed in a cyclical fashion, every 25 seconds it would start spinning like hell for 5 seconds and go back to normal speed (so 25secs normal speed, 5secs crazy, 25 secs normal speed, 5secs crazy and so on).

I have a 3D-rendering workstation with 4 gpus installed, 2 of which are the exact same card : Asus 2080TI turbo (blower).
One (card A) is my display card and is installed in the 1st pcie slot (near the cpu).
The other (card B) is a computing card and is installed in last pcie slot (near PSU).
2 other graphic cards are in-between.
Problem is with card B

I didn’t spot this behaviour until recently, now that I am working on a heavier 3d-scene with longer per-frame rendertime (this is important to understand the circumstances).

My 3D render allows all the cards to work together simulteanously on the same frame, so the more cards are rendering, the quicker the frame is rendered.
I am using false numbers here but just to explain the problem :
until now I was rendering many “easy” frames, for instance 100 frames that take 1minute each, no problem.
Now I am dealing with another kind of rendering task, 10 frames only but 10 minutes each.

Total render-time is the same but in the second scenario I have this weird behaviour of one card (the one near the psu) would have a huge increase in the fan speed for 5 seconds every 25seconds when rendering.
Since I don’t have this behaviour with shorter render-times I first thought that this would be related to the gpu temperature : more computing = more heat (when rendering shorter frames, the card have a short time in-between 2 frames to cool off while the frame is being prepared for render)……. but on the contrary, the card with the crazy fan is the coolest card from the rig, because being all the way down the case, it’s the only card that is not “breathing air” from the back of another (hot) card.
Here are some interesting numbers comparing card A (cpu side, normal blower behaviour) and card B (psu side, crazy fan) when rendering.

gpu usage : 100% A 100% B
gpu temp : 85°c A 76°c B
fan speed : 2600rpm (A all the time) 2100 (B by 25secs cycle) 4600rpm (B by 5 secs cycle)
power draw (from the board) : 173w A 224w B (why ???)

Fan speedup doesnt correlate with any change in gpu temp or power draw.
Cards are stock, no overclocking.

Speaking of overclocking, motherboard is a rampage v edition 10, I used to have a oc’d cpu but a while ago AIsuite refused to perform the overcloking and I just let it sit so with no OC, because I render with the gpu now, not the cpu, so I don’t really care anymore…... but still, if someone has an idea why I lost my oc (or maybe if someone thinks there can be a link with my gpu fan problem ?) : when I try to do a smart OC with aisuite now, I automatically get a blue-screen, no matter what.

But that was just a sidenote, the core of my problem is the crazy gpu fan. I mean….. the computer works fine but it is sooooooooo annoying for the ears ! (and also I wonder if the card is alright and safe)

Any idea ?