The best way to get rid of the squeaking noise is by applying a little bit of grease or WD40 on the suspension springs. We have come across a few cases where the springs got wet or moist and developed a little oxidation that then caused the squeaking.
If there is squeaking in front, take the front wheel out and detach the front mud-guard to access the springs. Apply WD40 or other grease directly on the spring coils. Have a look at this video (skip to 5:50): https://drive.google.com/open?id=11AHJjsoR5jvyxYxNapwTVouo1_erPEHp
(you do not need to remove the arms)
The same with the rear springs - these are right accessible when removing the bottom cover:
Have a look at this picture