New microwave trips circuit breaker?

My parents just bought a new microwave that is the same wattage as the one they are replacing. When they use it (in the same outlet) it trips the circuit breaker. They replaced the socket, no change. They tried it once in a different outlet and it worked (which is why they replaced the usual outlet) but they only did that once and the problem is intermittent. Thanks for reading my question and helping if you can.