id explain to him that as you are restoring it there will be a time when the angle grinder is not needed. id also tell him that it is not your aim to annoy him only to get the job finished, also that using an angle grinder and a small electric helicopter is perfectly within your rights as well as his. if he has had any building work done then you have just as much right to mention that and how you did not complain,
unless of course you did complain in which case are you surprised he's complaining)
he has a dog barking at all hours smokes weed at my back door where my kids play and i still dont complain lol