My arm was overextended and i heard a small pop sound. no swell or bruise, but when i move it fast some pain & the muscles seem to slide over the arm?

Strain: It seems you strained a muscle in the shoulder. Giving rest to the shoulder should resolve it . If not then you should see a physical therapist for treatment

Give it a rest,, : I don't know how you overextended your arm or how you move it fast to get the pain, but it likely needs some rest and slower movement and, above all, to avoid the movement that caused it to pop in the first place. You've likely pulled a muscle/tendon/ligament and it's likely ok but needs to get back into place and is likely inflamed. If the pain gets worse, see your doctor for an exam.

Possibly a strained: Tendon or sprained ligament. If d range of motion is ok i won't worry too much about it. Follow up with your doctor for any concern. You can apply ice packs for first two days then one packs. You can take over the counter nsaids for pain. Take care and god bless u! http://orthoinfo.Aaos.Org/topic.Cfm?Topic=a00111.