When we first start the 2014 Yaris, there is a grinding noise. We change the belts,but it still has not resolved the issue. When we turn on the AC before we start the engine, its not as bad. Any ideas on the issue.

Sound like the bearings are going out on compressor. Get ready to change it.

Could be a dry compressor bearing or possibly a pulley bearing or it could even be your belt tensioner. You said that once you turn on the A/C and apply the extra load to the motor, it quiets down. Thus, taking some of the strain from the affected bearing or pulley. If you take it to the Magic Mechanic, they will definitely be able to assist you. They have a great operation and all of their techs are extremely knowledgeable in all areas. Hope this helps...good luck!