Heatsink Fan running erratic

The fan is running erratic, have only done a full clean & PC was full of dust.

I did not replace or pull fan Heatsink from motherboard as (No PASTE) fan will spin freely but the fan on the sink makes a whirring noise now!

Any help please, Gigabytem/board over 8 yr old, AMD Phenom 555 CPU

[B]UPDATE: [/B]Problem Fixed – new fan & heatsink & 5 hours cleaning the power supply unit, never seen so much dust. Thank You all.