The upper 40mm fan makes a lot of noise. If I tap it, it goes away. Almost as if the bearing is going bad. I know these don’t have bearings, but you get the idea. It is vibrating off axis slowing the fan down until I get spinning full speed. Had many computers with the same thing happen.
You can try to unscrew a little screws which holding fan cooler, maybe it is tightened too hard.