This is a phenomenon that occurs due to previous physical impact, and if it occurs during use, it is not a defective product. If you hear a sound when you open the package, it is an initial defect, so please contact the store where you purchased it.
In order to check if your tumbler is still working and the vacuum seal is still intact, we advise you to fill the tumbler with hot water if the exterior becomes hot the vacuum insulation is no longer working, unfortunately, it is not possible to repair this.
Q. There is a sound coming from the inside of my tumbler when I shake it.
For more questions, please contact us via the contact form.