Thanks for coming to HCM. Painless sound from knee joint during movement after being in same position for long time can be a normal finding in most people but might be due knee joint inflammation
due to overuse or injury
. As you indicated that you were involved with standing job, it might be the cause. You can take ibuprofen
if you feel it is inflamed.
Orthopedic specialist can add their comments.
Wish you good health!