Stripes across the image BMPCC4K

Hi!
I recently purchased a used Blackmagic Pocket Cinema Camera 4K and noticed when using it in low light conditions that horizontal noise stripes appeared. The stripes seem to appear and disappear quickly across the image.
Can you tell me what it could be?
Looking at the images, does it seem like the condition is similar to that of all BMPCC4K cameras or is it a sign of a technical problem? Is it better to return it?
In the attachment I have uploaded a frame from a clip. (I pushed the exposure up to ISO 1000 to make it more visible, but the stripes are visible even at ISO 400)
I wanted to attach the original braw file but I can't due to size reasons.

If the posted image is ISO 1000 boosted to ISO 400 in post, you are very much underexposing your camera. With this camera as you may know, you have two ISO ranges, the ISO 400 and ISO 3200. Recommend you shoot and expose for either ISO 400 or ISO 1250 (which is the lower bound of the ISO 3200 range). I regularly use ISO 1600 safely but apply noise reduction in post. Never record using ISO 1000 by the way.

If you want a dark theme to your final image, expose close to normally in the camera with adequate light and then use the Colour tab to bring levels down to the darkness you want. You can set DaVinci Resolve to use HDR levels and that gives you six colour wheels and the Camera raw button to manage your tone plus an offset wheel that you might only rarely use.

thanks very much for the reply. I had increased it to ISO 1000 to make the defect of the stripes more evident. I was using it in low light and very underexposed to test the camera I just purchased in extremely low light conditions. If you confirm that the strips in these conditions are normal I won't worry about a possible malfunction.

I don't see anything unexpected there.

That's regular noise. Your image is underexposed. Use more light.

Thanks a lot to everyone. So everything alright