Uncomfortably Weird Feeling 6 Years After Saline Implants

I have Saline breast implants placed under the muscle. They are about 6 years old now. Once in a while throughout the years, I would bend down or do any activities, and feel a weird feeling like a movement inside my left breast. Now, all of a sudden, this feeling is there all the time. What could this be? I have no deflation and my breast have not changed its appearance. Both of them are much saggier than when I first got them but they have been like that for a way long time. Please help. I cannot find any answers for this discomfort in my breast (it's more uncomfortable than painful).Thanks