hey,

i'm a physio and i myself had my acl repaired with hams this year. 10th june to be exact. i experienced a similar episode to yours. the "guitar string plucked" in behind the knee. this is scar tissue from the remains of the semitendinosus muscle, which was used for the graft, basically tearing. its benign and in most cases will happen eventually. it shouldnt however lead to an effusion or swelling of the knee. the swelling of the knee might not be related to the hams issue. it may just have been that it flared up having gone to full weight bearing from partial weight bearing and thus increasing the loading on the joint. in this case just go back to first aid principles, compress, elevate, cool and rest. wait for the swelling to come down and go back to rehab at a slower pace. i myself had a few episodes during the first couple of months where i just did too much and paid for it by having to rest up for a week or so. hopefully thats all it is but of course if your not happy by all means consult your surgeon/physio. its too big a thing not to feel confident about your rehab