There are 2 of these rubber things either side of the boot, wind them out.
What this does, is when you shut your boot, it pushs the boot out and puts tension on the Latch. as the sqeeking is the boot lock vibration and rubbing against the latch when driving due to it wearing out. Doing this puts tension on the latch once again and stops that annoying noise.
10 second fix
) if the boot then becomes harder to shut after doing this, wind it in a tad 
