Question Odd laptop fan noise - no improvement after fan exchange

Jun 16, 2019
Hi, I'm struggling with odd behaviour of my laptop's cooling system (Dell Precision 7530). The fans make very annoying pulsating high-pitch noise, which affects my work a lot. It's not loud, but I use this machine mostly in evenings and quiet environment causes it to be noticable. Since, for the time being, I have a second unit, without this problem, I swapped the whole heat sink assemby (with fans) to find out that the problematic sound didn't dissapear. The other laptop, which got the fans form my unit, still doesn't produce this annoying sound.

So I have two identical laptops, same software/drivers, same conditions. And one producess this odd sound, which is not caused by the fans themsevles. Any ideas what the source of the problem might be? It's definitely related to the fans working and the sound characteristics match fan speeds. I thought it might have something to do with airflow outside the heat sink assembly, but there's really not much plastic there and I checked it thoroughly.