Hi Kevin,
I was wondering if Mitsubishi charged you for their initial visit? (we are in the east of England)
We have the exact issue that you have, new install in November '22 and since day 1 have had terrible noise problems. I liken it to a generator or a jet engine outside the house. Our installers agree there is an issue and have also been trying to get Mitsubishi to come out...I have numerous sound recordings since then and have sent them over to Mitsubishi, their engineers have apparently listened to the recordings and are saying its hard to tell what the problem is and we have to pay £350 for an engineer site visit. They said they will refund us if they find the problem is down to their equipment. I am really disapointed in this, we've already spent a lot getting the unit and installing and dont want to give them more money when there is clearly an issue with the unit.
This is also our second ASHP unit at our house, we have a larger Panasonic that runs separately and is very quiet in comparison.
I'm at a loss and it seems their warranty isn't worth anything in reality if they charge for a site visit.