Silent and Greedy (Silentcioso y Codicioso) Achievement awarded on escape, NOT WHEN escape arrives. Enemies (converts excluded) must not enter the fountain area throughout the entire heist. The alarm must go off before entering the bank. In the San Martín Bank job, let the heist go loud before anyone enters the bank and keep all enemies away from the fountain plaza until the escape is available on the OVERKILL difficulty or above.
Use the El Ritmo melee to kill any of the mariachi band members.
San Martin Bank Heist Now Hit Me with the Music This achievement guide shows PAYDAY 2: San Martin Bank Heist (update).