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Mitsubishi Smart Multi H2i is making hissing sound

hdp203 Member Posts: 3
Hi All,

I have 2 Mitsubishi MXZ-SM48NAMHZ units installed in my house a few months ago. Each unit is connected to 4 indoor units.
Everytime I turn on the AC. The outdoor unit is quiet for the first 5-10 minutes. Then starts making hissing noise (link below). This constant noise will turn off after a long period of time (1+ hrs) or when I turn off the AC.
The system seems to work fine (cooling the house).


For reference, I used a sound meter app to measure the noise, and it is ~65db when the phone is about 1ft from the outdoor unit. Not sure how accurate is the phone app though.

Is it something I should be worry about?