Whether or not to replace fan

[jehill39]

Background:

My HP ENVY x360 15m Convertible PC will be two years old on Memorial day.  Fan noise was negligible until recently.  Now it's annoying!  It's even more so because the predominant noise typically cycles between 129Hz and 140Hz (measured using e-scope3in1 cell phone app) once every two seconds.

How loud is it?  I didn't know what loud was until until I updated the BIOS in response to a "tip".  The fan is run at full speed several times during the process.  It appears to me that what I hear normally is the fan idling.

The service manual for this model indicates that it is necessary to remove the System board before replacing the fan.  It's not obvious why that's necessary.

Questions:

1.  Is it necessary to replace the fan?

2.  Is there cleaning that may be done with the fan removed to eliminate the noise?

3.  Is it safe to remove/replace the fan without removing the System board?

[jehill39]

i have pretty much convinced myself that the answer to Questions 1 and 2 is "No".  I opened up the unit again and took another look.  There is no trace of dirt anywhere.  I took the following photo below.  I counted the number of blades on the fan.  There are 37.  That means that the 129Hz - 140Hz speed range observed corresponds to 209 rpm - 227 rpm.  That's really slow.  The blade spins freely when i spin it by hand.  Apparently, the source of the noise is pulses of air.

[jehill39 · Accepted solution]

i guess that there is only one way to answer Question 3.  Attempt fan replacement without removing the System board.  I'll wait until I can't tolerate the noise before I do that, because the fan is working fine other than the noise.