Hi. After some pointers as I have looked at a noisy unit this morning. The customer told me it makes a whistling noise a few times thought the night that lasts for 4/5 mins. I have checked the unit on all fans speeds and am pretty sure it's not the fan. Then turned the temp up and down to get the expansion valve to open/close it did make a very faint whistle while opening at one point. The system is a toshiba vrv MMY-MAP0801T8-E indoor unit is MMD-AP0071SPH Any thought on what would cause the expansion valve to whistle intermittently?
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