Okay, let's break down what's happening and what to do. You're right, buzzing from the switch and flickering lights are a sign of a problem, and it's good your wife caught it. Ignoring it could lead to a fire.

Understanding AFCI/GFCI Breakers (Since you mentioned QO220CAFCI)

Your breaker is a Square D QO220CAFCI, which means it's a Combination Arc Fault Circuit Interrupter (CAFCI) breaker. It's designed to protect against two main types of electrical faults: Arc Faults (AFCI)

These are dangerous sparks or arcs caused by damaged wiring, loose connections, or failing appliances. They can ignite surrounding materials. AFCI breakers are designed to detect the signatures of these arc faults (specific patterns of current and voltage) and trip before a significant fire hazard develops.

Ground Faults (GFCI)

These occur when electricity leaks from the intended circuit path and finds an unintended path to ground. This is a shock hazard. GFCI breakers detect this leakage current (even a very small amount, like 5 milliamps) and trip rapidly. GFCIs are important in kitchens, bathrooms, and outdoor areas.

Why Didn't the Breaker Trip?

This is the critical question. Here's why it might not have tripped, even with flickering lights and a buzzing switch:1. The Arc Wasn't "Big" Enough/The Right Type

AFCI breakers are designed to detect specific patterns of arcing. A small, intermittent arc in a switch might not meet the trigger criteria for the breaker to trip. The arc fault might be subtle enough that it doesn't generate the specific signature the AFCI is looking for. AFCI breakers are very sophisticated, and their operation can be affected by the quality of the connections and type of load on the circuit.2.

Faulty Breaker

While rare, breakers can fail. They can become less sensitive over time or have internal defects. This is why testing is important (more on that below).3.

The Problem Might be Primarily a Loose Connection

Loose connections can cause flickering and buzzing, but they don't always create a full-blown arc fault that the AFCI breaker detects immediately. However, loose connections are a HUGE fire risk because they increase resistance, generate heat, and can eventually lead to arcing.4.

Load on the Circuit

The load on the circuit can sometimes affect the breaker's sensitivity, although this is less likely with modern CAFCI breakers.

What You Need to Do Immediately

Turn OFF the Breaker

Go back to your electrical panel and turn OFF the breaker supplying power to the circuit with the flickering lights and buzzing switch. Do this now. Leaving it on is a fire hazard.

Do Not Use the Circuit

Keep the breaker off until you have investigated and repaired the problem.

Troubleshooting and Repair Steps1.

Replace the Switch

This is the first and easiest step. The buzzing sound strongly suggests the switch is failing.

Important

Turn off the breaker BEFORE working on the switch. Buy a quality replacement switch (same amperage rating as the original). Carefully disconnect the wires from the old switch and connect them to the new switch. Make sure the connections are tight and secure. Pigtail ground wires together. If the wires are backstabbed (pushed into holes in the back of the switch), release them properly. Backstabs are a common point of failure, and it's generally better to use the screw terminals. Use wire nuts on all connections, even if the new switch has screw terminals.2.

Inspect Wiring Connections

While the breaker is off, systematically check all wiring connections on that circuit:

At the Light Fixtures

Check the connections inside the light fixtures that are flickering. Look for loose wires, burned insulation, or signs of overheating.

In Junction Boxes

Open any junction boxes on that circuit and check all wire connections. Tighten any loose connections.

At the Breaker

After ensuring power is off (use a non-contact voltage tester), carefully check the connection of the wire to the breaker. Make sure it's tight. Use proper wire nuts and electrical tape to ensure secure, insulated connections.3.

Test the AFCI Breaker

Most AFCI breakers have a "TEST" button on them. After you've replaced the switch and checked the wiring, turn the breaker back on and press the TEST button. The breaker should immediately trip. If it doesn't trip when you press the TEST button, the breaker is faulty and needs to be replaced.4.

Monitor After Repair

After replacing the switch and checking the wiring, turn the breaker back on. Closely monitor the lights and the switch for any signs of flickering or buzzing. If the problem returns, there's likely another issue on the circuit, and you may need to call an electrician.5.

Test the continuity of the ground circuit: This is a safety item that should be tested. A wiring problem that impacts the grounding system can present a shock hazard.

When to Call an Electrician

If you're not comfortable working with electricity. Electricity is dangerous, and it's better to be safe than sorry.

If the problem persists after replacing the switch and checking the wiring.

If the breaker fails the TEST button test.

If you see any signs of burned wiring or overheating.

If you are unsure about any of the steps above.

Important Safety Notes

Always turn off the breaker before working on any electrical wiring.

Use a non-contact voltage tester to confirm that the power is off.

Wear appropriate safety gear, such as insulated gloves and safety glasses.

If you're unsure about anything, call a qualified electrician.

Check your local electrical code for specific requirements.*You were absolutely right to be concerned, and your wife was right to alert you. Addressing this promptly is crucial for preventing a potential fire. Good luck! Flag for review