The new audio amp in the V4 uBITS is a very common design in inexpensive audio equipment for many years. It could be sensitive to power supply voltage levels and if you are using it at below its design supply voltage it may not have enough bias current resulting in crossover distortion. The 2 solutions would be to make sure you have the proper minimum voltage applied or re-bias the outputs...add a third diode, or use a potentiometer in place of the diodes so the bias can be adjusted. In higher power systems, the 2 diodes would be in physical contact with the output transistors and would self adjust the bias as the transistors heat up to reduce the chance of thermal runaway.??