How to wire an inverter?

I have a Magnum inverter and I'm not particularly happy with it. It makes an irritating hum when it is on. Loud enough to keep you awake. The hum gets louder as the load increases, but is quite audible even with no load. I would like to use it to charge the computer and cell phones etc., but try not to because of the noise. Magnum technical support says "yeah, they do that". Their charge monitor doesn't work well either, not accounting for its own load on the battery.

I've not had the best of luck with Xantrex either - though it depends on the product. Xantrex is the amalgamation of a bunch of companies they acquired. The best inverters are Mastervolt and Victron, but expect to pay for them.