I had nice sleek and trendy Mitsubishi 'through the wall units' in my overseas property. They were about as pleasing to the eye as you can make a wall mounted refridgerator (and let's be honest, they are no worse than having a radiatior or combi boiler stck to your walls back in the UK). Never had a problem with noise or leaks, I guess it is down to how well they are installed and how much you pay for a quieter motor in the unit?
