Hey, what you are looking for are zero-cogging servos. These range from motors with skewed magnets or stacks to slotless motors. Both are less torque dense. Slotless motors are great for low cogging harmonics which are a typical noise source, but torque ripple is an issue. Pair with a driver that has >24kHz switching frequency and carefully tune the torque loop to eliminate significant ripple.
You may have a hard time finding these already in housings, Kollmorgen and Celera Motion make frameless kits for $$$. If it's silent for hobby use... let us know if you find it!