I've had several variations on this problem in my garage, which indeed did once nuke everything in the garage freezer.

CAVEAT: I'm not a licensed electrician. If you follow my advice and electrocute yourself, it's not my fault. Don't mess around with 120V.

- Any semi-modern up-to-code wiring will require that there's a GFCI on every circuit. It's there. Look for it. I think my house has precisely one non-GFCI outlet, hidden in a strange corner in the attic. And even then, I'll bet I just never found the GFCI.

- It's reasonably typical for electrical plug boxes to be wired sequentially. The first one on the chain is typically where they put the GFCI outlet. That outlet and every one after it has one wire (three conductors) in and one wire (three more conductors) out. As Heather mentioned, it can get crowded in there, and and things don't always get screwed down properly.

- Furthermore, GFCI outlets, unlike standard ones, have an "upstream" and a "downstream" side, i.e., the path to the circuit breaker and the path to the rest of the outlets on the chain. Older GFCI outlets will happily let you install them backwards, and you won't be protecting any of the downstream outlets. Newer ones flat out don't work if you wire them up backwards. (Of course, you have no idea if your original electrician got it wrong, and of course the two wires aren't labeled. If you've got a multimeter, make sure the bare leads are poking out and not touching anything else, then energize the circuit and probe them. Carefully. Then turn the circuit off again.)

- Another way that electricians can screw up is by installing the GFCI somewhere other than at the head end of the chain. They only protect "downstream" outlets. If you're in a modern up-to-code house, you can get a cheap electrical outlet tester (here's one from Home Depot; note the red "test" button). A proper home inspector goes to each and every outlet in your house, plugs that thing in, hits the "test" button, and is expecting a GFCI somewhere to pop. If it doesn't, and instead your circuit breaker pops, then the house is not up to modern code.

- If you want to be paranoid, then replace that GFCI once you find it. They tend to wear out after ten years. We had one in our bathroom that had a quiet 60Hz buzz. I replaced it. No more buzz.