Five years post implants, sloshing sound in breasts - what could cause this?

Answer from Dr. Sean Hill, Board-Certified Plastic Surgeon at Lone Star Plastic Surgery – Frisco, TX:
Great question, and one that can sound a bit alarming when you first notice it! The sloshing or gurgling noise you’re describing is not uncommon, and in many cases, it’s not a sign of anything dangerous, but let’s break it down.
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Do you have silicone or saline implants? If you have saline implants, you may just be hearing the saline solution within the implant; or the implant may have ruptured. Normally when that happens, the saline leaks out, and your body just reabsorbs the saline, but over the course of time, you would notice that breast decreasing in size as more saline leaks out.
Another possibility with either saline or silicone implants is fluid developing around the implant. I would recommend following up with your plastic surgeon to be evaluated. If he/she has an ultrasound machine, that can usually be done right there in the office, which would be a quick and easy way to evaluate for fluid around the implant.