Any case will absorb some sound, some even have sound absorbing matte just for that, but as mentioned above, it all depends on exactly what's in the case. There is only typically 2 sources of sound from components. Fans and drives. If you have multiple fans, it'll be slightly louder, if you are pushing the limits of cpu, gpu, psu those fans will make it louder, crappy high rpm fans, louder still. And then there is the hdd. If that's all you have, it runs constantly, making noise, if you primarily use an SSD, it'll be quieter as they make 0 noise. Stock cpu fans are very loud under load, good aftermarket cpu coolers typically run quieter as their TDP is generally higher than stock coolers so almost never run their fans at 100%.
Like he said, it's what's inside, what's inside and what you are doing.