It is likely to be one of three issues in my opinion
My suggest would be to pull the unit out and run if for a couple of hours and see if it gets cold, if it does you need to look at how you can increase the circulation to the back of it, eg not pushing it far back or leaving a gap to either side.
Secondly the thermostat, depending on the model some have different chiller settings, if they do change the settings to the coldest option and see if it makes more of a noise, then after 10 minutes change it to the lowest setting and see if it get quieter. If it does this proves its detecting the need to cool the inside, if it doesnt it worth getting someone out as the part often costs less than £10.
Finally the last set of issues would be very costly, there isnt much you can do in these areas, and would suggest you look at replacement rather than repair.
I wanted to check if you still require support, or if your happy for the case to be closed.
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