Question nh u14s 2nd fan causing high pitches noise

[AscendantLag]

so i bought a second fan for my nh u14s and when the fan is attached to heatsink it makes a loud whinning noise but if i take it off even at full rpm nothing. Whats causing this

 

[CountMike]

so i bought a second fan for my nh u14s and when the fan is attached to heatsink it makes a loud whinning noise but if i take it off even at full rpm nothing. Whats causing this

Is it identical to first one ?