Okay, let's break down this AC condensing unit noise and the potential causes, along with what you can do about it.

Understanding the Noise

You describe the noise as a "transformer hum, but more pronounced." This is helpful. Possible causes:

Compressor Vibration/Resonance

The compressor itself could be the source. Internal components (pistons, valves, etc.) vibrate during operation. Over time, wear and tear, or even just the natural frequency of the components, can amplify these vibrations, creating a noticeable hum. The intermittent nature could be related to the compressor's workload or the specific position of internal parts during its cycle.

Contactor Chatter

The contactor is the electrical switch that turns the compressor on and off. Sometimes, the contactor can chatter or buzz, especially if it's worn or if the voltage is fluctuating slightly. However, a typical contactor chatter often has a different kind of sound, more like a "click-click-click."

Fan Motor Issues

While you're focusing on the compressor, don't completely ignore the fan motor. If the fan blades are not properly balanced it can introduce a noticeable noise during operation.

Loose Components

Check for loose mounting bolts, refrigerant lines, or panels. Vibrations can cause these to rattle and amplify the noise.

Refrigerant Line Vibration

Refrigerant lines, especially those close to the compressor, can vibrate significantly. If they're touching something (like the cabinet or another line), they can transmit a humming/buzzing noise.

Electrical Noise (Less Likely)

While less likely, it's possible, especially with slightly high voltage. Sometimes, electrical components can emit a hum, particularly if they're under stress.

Addressing the Issues and Troubleshooting

Here's a systematic approach:1.

Visual Inspection



Check Voltage

You already have voltage readings. 245V is on the high side but probably within tolerance. 208/230 units can typically tolerate up to 10% over voltage. However, prolonged operation at that level could potentially shorten the life of the unit, especially the compressor and capacitor.

Capacitor

If you are comfortable and know how to discharge it, look at the capacitor. Is the top bulging? This indicates it is failing.2.

Isolate the Noise



Careful Listening

With the unit running (and preferably with someone assisting you), try to pinpoint the exact origin of the noise. Is it coming from the compressor itself? The contactor area? The fan motor?

Gentle Pressure

While the unit is running and with extreme caution, you can try gently pressing on different components (refrigerant lines, the compressor housing, the cabinet).

DO NOT TOUCH ELECTRICAL CONNECTIONS! Use insulated gloves and be extremely careful. If the noise changes or stops when you apply pressure, that can help identify the source.3. Component Checks



Capacitor

As stated before, check the capacitor. This is a common failure point. It should look perfect. If you can afford it, consider replacing it anyway. Capacitors are cheap, and they may be affecting the performance of your compressor.

Contactor

Inspect the contactor. Look for signs of burning, pitting, or damage. If in doubt, replace it. They are inexpensive and easy to replace.

TURN OFF POWER BEFORE REPLACING. Fan Blades

Inspect the fan blades. Are they damaged or have any pieces missing?4.

Maintenance



Cleaning

A dirty condenser coil can cause the unit to work harder, potentially exacerbating noise issues. Clean the coil thoroughly using a garden hose with a low-pressure nozzle. Spray from the inside out to avoid bending the fins.

Tighten Connections

Check all electrical connections at the condensing unit and at the service panel (where the breaker for the AC is located). Loose connections can cause voltage drops and electrical noise.

Lubricate Fan Motor (If Applicable)

Some fan motors have oil ports for lubrication. Check your unit's documentation or the motor itself for lubrication instructions.

Important Safety Notes



Turn off the power

Always turn off the power to the condensing unit at the breaker before doing any inspection or maintenance.

Discharge the capacitor

The capacitor stores a dangerous electrical charge, even when the unit is off. If you're going to touch the capacitor, you must discharge it properly using a screwdriver with an insulated handle. Search on YouTube for specific instructions.

Be aware of moving parts

The fan blades can cause serious injury.

When in doubt, call a professional

If you're uncomfortable working with electricity or refrigerant, or if you're unsure about any of these steps, it's always best to call a qualified HVAC technician.

Is It a Dire Situation?

Based on your description, it doesn't sound like an immediately catastrophic situation, but it is a sign that something isn't quite right. Ignoring it could lead to premature failure of the compressor or other components, which would be a much more expensive repair. Addressing it now could extend the life of your unit.

Recommendation


Start with the visual inspection and cleaning.2. Attempt to pinpoint the source of the noise.3. If you're comfortable, replace the capacitor and inspect the contactor.4. If the noise persists, or if you're uncomfortable with any of these steps, call a qualified HVAC technician. Provide them with as much detail as possible about the noise, your voltage readings, and the troubleshooting steps you've already taken. Flag for review