The vref at 0.4v gives 0.8A so you're running those motors at/near their maximum current handling, they will always be noisy when near that level. The document above has values of vref against current. You should always aim to run motors at around 75% of their max current to prevent excess noise, and heating of the motors in use, which can soften/melt printed motor brackets. For your motors reduce vref to 0.3v or even 0.25v. See if that helps with noise.
The issue with 0.85A motors is that they may not provide enough torque to move larger/heavier printer axes, especially corexy where one motor has to be able to move the entire corexy mechanism by itself on diagonal head moves. 1.68A motors are more commonly used, as most drivers can deliver 1.2A (vref 0.6v on these drivers) maintaining the 75% recommended setting and will generate at least twice the torque.
Also check the jumpers under the drivers carefully to ensure they are set to the microstepping mode you want i.e. 1/16 is the most common setting or 1/32 if your controller can handle it. If they are set to 1, 1/2, 1/4 or 1/8 they are likely to be noisier. The document linked to there shows you the jumper config you need.
If you are not sure what they are set to, ask for 50mm of movement, if your firmware is using the default steps/mm for example 80 for 20t pulleys and gt2 belt and 1/16 microstepping it will move 50mm, if it moves 100mm then its set to 1/8, if it only moves 25mm then its set to 1/32. Adjust your steps/mm to the correct amount for the microstepping you are using.
I'm not sure I'd "measure" resonance but some frames vibrate at certain frequencies, sometimes its loose tnuts/bolts etc... Though I suspect you are just over driving your motors.
The issue with 0.85A motors is that they may not provide enough torque to move larger/heavier printer axes, especially corexy where one motor has to be able to move the entire corexy mechanism by itself on diagonal head moves. 1.68A motors are more commonly used, as most drivers can deliver 1.2A (vref 0.6v on these drivers) maintaining the 75% recommended setting and will generate at least twice the torque.
Also check the jumpers under the drivers carefully to ensure they are set to the microstepping mode you want i.e. 1/16 is the most common setting or 1/32 if your controller can handle it. If they are set to 1, 1/2, 1/4 or 1/8 they are likely to be noisier. The document linked to there shows you the jumper config you need.
If you are not sure what they are set to, ask for 50mm of movement, if your firmware is using the default steps/mm for example 80 for 20t pulleys and gt2 belt and 1/16 microstepping it will move 50mm, if it moves 100mm then its set to 1/8, if it only moves 25mm then its set to 1/32. Adjust your steps/mm to the correct amount for the microstepping you are using.
I'm not sure I'd "measure" resonance but some frames vibrate at certain frequencies, sometimes its loose tnuts/bolts etc... Though I suspect you are just over driving your motors.