This sound can occur due to prior physical impact and does not indicate an initial defect if it happens during regular use.
However, if you hear a sound at your first usage, this may indicate an initial defect.
In that case, please contact the store where you purchased it.
To check if the tumbler’s vacuum seal is still effective, fill it with boiling water.
If the exterior becomes hot, the vacuum insulation is compromised.
Unfortunately, this cannot be repaired.