I thought it was tightening at first, dismantled everything, tightened everything super tight, but still happened couple days later, I then switched over the legs because it may be those, however it still happens on left side.
Basically it must be the frame causing the noise.
Should I put some paper where the noise is to see if that fixes the problem?
that's what i would do. try to shim the area where the noise is coming from. also, make sure the desk is level by adjusting the black feet on the legs.