I am going to clean my computer. First I want to oil my fans (CPU, GPU, and case fan). I don't have any machine oil. Can I use oil from kitchen (sunflower or rapeseed) to oil them?
NO NO NO NO
Cooking oil will "gum up" after a while and the fans will literally stop spinning.
Machine oil is better, but even then, it can catch dust and ultimately increase friction.
Your best solution is simply to replace the fan, if it is noisy.
If you're looking for noise reduction, lowering the fan speed is the best method. Fans are cheap and putting moist things inside them (like oil, though it technically isn't a liquid) may result in temporary improvements, but these are offset by problems from attracted dust and the like.
The nicer fans don't even had a physical connection between the blades and motor, and the spindle and fan housing, as they use magnets to hold the two units separate. No touching means no lubing.
Vibrations in the case are due to imbalance, not bad contact. And imbalance is fixed using a file (if you're patient and OCD) or a credit card (if you're not). Higher quality fans are better balanced, and and magnetic bearing fan with the maximum possible diameter will allow for the quietest long-term operation.
We use oil to reduce friction.
Up to some extent we can use sunflower oil, but if you can arrange some drops of bike engine oil or any vehicle engine oil then it works better.
If you have a bike, then after servicing, its engine oil is replaced. If you have that, it would be good.