Sorry to hear that, that sucks!
When you say, you "tested the voltages on all the outlets in the house", how exactly did you do that?
If you're welding, I'd bet the farm either one of the other outlets in the house is wired incorrectly, or an extension cord if you used one or more. Something is wired wrong - either Hot to Neutral, or worse yet, Hot to Ground.
If you tested the voltages by sticking the probes from a voltmeter into the hots and neutrals of the receptacle only observing the voltage reading that's only a partial test. You need to observe the voltage from hot to neutral, hot to ground, and neutral to ground to be thorough on each receptacle. [you may very well know this, but for anyone else who might stumble across this thread in the future] On a standard 15-amp grounded (3-prong) Edison receptacle, the smallest slot is the hot, the slightly larger slot is the neutral, and the ground is pretty obvious. If you don't have a receptacle tester, you should get one.
And I'm sorry to say - for future reference, you could easily run almost any home recording gear and a small PA on a single 15 or 20 -amp circuit as you would find in most homes. - Two circuits at the most. Pulling everything from all over the house introduces the potential for things like this and more ground loops etc.
Do some more testing and let us know what you find.