Prove it... (Score 1)

Lots of good feedback already (no pun intended), but in addition to phase cancellation or documenting the noise with a db meter, you could also record it. Grab a copy of http://audacity.sourceforge.net/ to visually show what's going on, and if you're still not believed, pitch-shift it down an octave or two and play it back. I guarantee they can hear 4,250Hz (I still can and I turned it off 30 seconds ago. Doh!). If you simply can't get anyone to believe it's bothering you, plan-b is to disable it. Before you get a BB gun involved though, I'd try to just cut the power or turn it off. As has already been said, if he can't hear it on - he can't hear it off. I have a similar (but tougher I think) issue that I might need to officially ask Slashdot - about light pollution. My yard would be a near perfect place to see astronomical events if it weren't for my neighbor's bazillion-watt mercury vapor light. He's already said he won't turn it off, and he's literally the stereotypical "pissed-off old guy with a shotgun" that lives next door. If you tripped and fell into his yard from mine, he'd be in the backyard with a gun yelling at you (he always yells as he's deaf, but wants to make sure you hear him). I'll admit that I haven't looked into his or my legal rights regarding the subject, but this thing is bright enough that everyone in the fam' that has a bedroom on that side of the house has to close their (room-darkening) blinds at night to get any sleep. I know the bulbs for the thing cost a fortune, but I haven't been pissed off enough yet to shoot the thing out. Oh - he also burns his garbage. A wonderful aroma with the windows open on a warm summer's day. I won't go into that one.