I noticed that the fans in my 15” 2016 “Touchbar” MacBook Pro have been making a strange rattling sound when they spin up, so I decided to open it up and investigate. The first thing I noticed was the dust build up on the fan blades, which was surprising for 2 months of normal use. This might be due to the “split-blade design” Apple uses on their 15” MacBook Pro fans.
The split blade design basically means that half of the fan blades on each fan are smaller and spaced in such a way that they slot into the wider gap left by the larger blades. According to Apple, this allows them to fit more blades in the same fan diameter (70 blades vs 50 on the 13” Touchbar MacBook Pro without the “split blades”) and should increase air flow per revolution. I think it would be interesting to test whether split blades are actually any better than normal blades, but I don’t have the equipment to test this so hopefully someone out there could shed some light on this.
Cleaning out the dust build up using a cotton bud and vacuum cleaner (making sure that the fan is kept stationary to avoid burning out the motor) solved the rattling problem completely. The rattling was possibly caused by rotor instability, as dust would have caused the fan to become unbalanced at higher RPMs. Although system temperatures remained the same as before, RPM has decreased after cleaning indicating that the fans are doing a better job of cooling the system down.
This is the second time I had to clean out the fans due to this problem. Usually it takes about 2 months for dust to build up enough to noticeably affect cooling and noise performance. The smaller gaps and larger surface area of the fans may be contributing to the faster dust build up on the blades, in some cases blocking the airflow completely. I’ve never seen this problem arise so quickly in my previous Mac notebooks (without split-blades), so this is my best guess. Either Apple needs to optimise their cooling design in their next iteration, or I just need to get the duster out more often.
In the meantime, I’m thinking of a small modification to add an easy to clean/replace filter on the air intakes without affecting cooling performance.
ATR93 