The left side
The Hard Disc Drive (HDD) is located at the left side. Firstly, remove the cover, as this is a clip fit it can rattle, which causes a loss of sound definition.
As the upper part of the opening is a bit weak, attach Teflon tape from the metal part of the HDD, to the plastic part of the side frame, this will reduce resonance.
The joint of the upper case and lower case can be seen at the centre, note that no treatment is necessary here. If Teflon tape were attached there, the sense of S/N ratio may increase, but the feeling of air or atmosphere would be reduced.
In fact, if this joint area were to be totally treated with Teflon tape, you would find the sound would become very 'dead'. Of course, if you prefer this sound character, please experiment for yourself.
I would advise you not to attach tape to the opposite side, which is the right side with ventilation hole. This appears to contain a 'floating' structure, which is actually quite complex and appears to be for cosmetic reasons. According to my evaluation, if any part is fixed with tape the sound becomes worse. In this case there are possibly some portions which actually suffer from vibration due to tape adhesion.