Question PC fan is making a knocking noise ?

[Eamonn100]

I have 3 PC fans plugged in to a single header...

2X... Noctua industrialPPC NF-F12 iPPC-3000 PWM 0.30 A
1X... Noctua industrialPPC NF-F14 iPPC-2000 PWM 0.18 A

Intermittently one of the 120's makes a knocking noise on start up and stops spinning sooner than the other two. When the knocking noise doesn't happen, all 3 stop at the same time.

I have removed the fan from the case to eliminate any possible knocking due to improper mounting issues.... Why would it be intermittently making a knocking noise?

 

[Roland Of Gilead]

Hey there,

Perhaps the bearings are loose or the fan itself is damaged and rubbing off the chassis of the fan.