Is it normal to hear sloshing sounds after breast augmentation?

The sucking sound that you are hearing is simply trapped air around the outside of the implant that is causing a type of vacuum.  This is not common, but I have heard this complaint before and usually lasts 1-2 weeks.  Don't worry about it, but obviously make sure to discuss it with your plastic surgeon to be sure.

It is difficult to give you an accurate answer without knowing, what type of implants you have, gel vs saline. The incision placement , periaerolar, infra-mammary or trans axillary. Also, how much swelling did you have and did you have any post operative bleeding.

Saline implants may slosh for a while after surgery if the air bubbles have not been removed, much like a water bed, this however, resolves quickly.

If you had a trans-axillary approach to place the implant. this makes a large track, and may make a sucking noise when you lift you arm. Additionally, if the pocket was made quite large this could create a space that could make a sucking noise. Sometimes fluid around the implant can make a squeaking noise. If there is not a heamatoma ( a large collection of blood)  or a seroma ( a collection of fluid) this should resolve quickly.

When placing the implant, the pocket sometimes has air in it, and the surrounding skin will feel like crunching snow when you press on it, this is known as subq-emphysema. This effect also resolves quickly.

It is not uncommon, in the immediate post operative period to feel that something will happen to your implants, like they will pop, get cold, or pop out if you are to active. It takes about six months to subconsciously integrate in your mind, that they are part of you and feel more like you body.