A soft lump on the left clavicle appears only 1 day every while_ non-pulsating .... there is history of simple multinodular goiter?

Unrelated: I don't know what would be causing a soft lump to appear intermittently on your clavicle. Maybe it is some skin inflammation or a reactive lymph node. It should have nothing to do with having a simple multinodular goiter.

The only medium: That changes size that rapidly and recedes are air and fluid. In this location it is most likely a congenital cyst such as a branchial cleft cyst. You need to be seen by an otolaryngologist.