Cleaning won't usually fix a bearing in a fan once it is bad. You have to change the fan. It's easy to find: run the machine with the side cover off. Listen closely to where the noise is coming from and some of the fans you can place a finger tip on them briefly right at the centre so you don't get hit by the fan blades. It's harder with the PSU fan or front case fan.
30 minutes suggests that the bearing warms up and now it is good until the next cold boot. Once you figure out which fan it is you can leave your PC running until the new fan comes in.