The green sheathed wiring, especially on the back side of a fridge, near the bottom of the frame, most likely culprit.
If you reset your GFI breaker for the garage, unplug this refrigerator, and plug in only the freezer, which worked fine before, does it still trip?
If not, I'd suspect a problem with the refrigerator itself, especially since if I recall correctly, you mentioned it was used, and that you transported it yourself.
Although it is true that both such appliances (freezers and refrigerators) can cause nuisiance tripping on Ground fault protected circuits (mostly due to their current draw and current fluctuations when either the compressor motor or heating element kicks on - frost free appliances) if the circuit is properly rated (amps sufficient for start-up of inductive load - motor loads and wire size - not overheating) and especially since you indicated a ground fault protective circuit breaker - you shouldn't have this difficulty UNLESS there is a true fault situation which I suspect IS LIKELY due to used appliance recently installed in a garage - where no other difficulties were previously experienced (especially with the freezer).
Dampness in the garage combined with a bad ground connection - especially to the case - could be an ACTUAL fault occuring and NOT NUSIANCE TRIPPING!!!!
Again, I would take this appliance out of service until/unless you can ASSURE this is not the case.
How many circuits to this garage? Attached or unattached to your home?
What is the Amperage of this circuit - 15 or 20 Amps?
It might be, especially since it is a GFI Circuit breaker - that your circuit has too few amps and/or the wiring is undersized and an under-voltage/overcurrent situation is occuring!!!!
If your circuit amps are correct for this refrigerator and the additional load on the circuit - and you have an undervoltage situation (could fluctuate - i.e. be fine one time you test, be low later) your motorized load will attempt to draw MORE amps to compensate.
If your circuit is undersized in the first place (MANY refrigerators NEED 20 amp circuits these days, some will do okay still on a 15 amp circuit but cannot SHARE it as will oftentimes draw more than 12 amps during a motor start AND a defrost/anti-condensation dryer cycle within). If another appliance, especially another motor load (freezer) is drawing a start up or continuous run at the same time - the result might be exceeding the trip limit on your Circuit Breaker.
Point being, without more information it would be entirely inappropriate to ASSUME you have merely a nusiance trip situation, given what information you DID provide.
There should be information regarding initial and run amps somewhere on this appliance, as well as the freezer.
Also you'd have to know if your CB (GFI protected) is rated at 80 or 100 percent.