Discolouration of a casing is not grounds for a RMA. Have you tried wiping it clean as it could be oils from your hand?
The SSD should not be buzzing since there are no components that are physically able to generate audible sound. Are you sure it is from the SSD? It might be your PSU, video card, or motherboard. A trick is to get a paper towel or toilet paper cardboard roll and hold it against your ear. Then point the other end around your case. This will help isolate noises and assist in determining the source of the sound.