What Causes Crepitus In Knee After Acl Reconstruction Surgery?

hello i had my acl reconstruction surgery with a hamstring graft 4 weeks ago and i am starting to walk without crutches but i have persistent crepitus in my knee especially medially , what are the possibilities and is this something i should worry about noting that they are almost painless ( the normal sensation of crepitus) but once in a while it hurts a little . THANKS