Okay, I've reviewed the (temporary) video and listened to the sound. Based on the information given, and assuming the noise is indeed coming from the motor, here's a breakdown of potential causes and troubleshooting steps to further investigate the noise, specifically considering the "apartment above" situation

Understanding the Noise and Likely Causes
Switching Noise (PWM)

The most common source of noise from a VFD system is the Pulse Width Modulation (PWM) carrier frequency. It's a high-frequency switching action that controls the voltage to the motor. You've already tried increasing the carrier frequency, which often reduces audible noise, so we need to consider why that didn't work. It's possible the motor is particularly sensitive to the specific carrier frequencies you tested.

Mechanical Resonance

The motor itself could be vibrating at its resonant frequency, or the frequency of other components nearby. These vibrations can amplify within the motor's housing and transmit sound waves.

Loose Components

Any loose component, such as the fan in the VFD or the motor, mounting bolts, or nearby objects, can rattle and amplify the noise.

Motor Windings

Less common, but possible, are issues with the motor windings themselves. Loose windings or insulation breakdown can create a buzzing or humming noise.

Harmonics

The VFD creates harmonics in the current that can interact with the motor and create noise. These harmonics may also cause mechanical vibration.

Grounding Issues

Poor grounding can create circulating currents and contribute to noise.

Magnetic Saturation

If the motor is running near saturation (especially at low speeds), it can produce more audible noise.

Load

The specific load connected to the motor could be contributing to the vibration.

Troubleshooting Steps (Prioritized for "Apartment Above" Sensitivity)1. Confirm Noise Source and Transmission Path



Isolation

This is CRITICAL! You need to be absolutely sure the noise is coming directly from the motor/VFD and not some other equipment in the room. Try running the VFD and motor with no load attached. Does the noise remain? If not, the load is part of the problem.

Stethoscope/Listening Tube

Use a mechanic's stethoscope (or even a piece of hose held to your ear) to pinpoint the exact area on the motor, VFD, and connected equipment where the noise is loudest. This can help you differentiate between motor noise and VFD noise.

Vibration Analysis (Ideally)

Vibration analysis is the best way to identify resonant frequencies and mechanical problems. A vibration analyzer can pinpoint the frequency and amplitude of the vibrations.

Transmission Path

How is the noise getting to the apartment above? Is it traveling through the floor directly due to vibration? Is it airborne sound waves traveling through the ceiling? Knowing the path is crucial for mitigation.2.

Motor Isolation and Damping (Immediate Priority for Apartment Noise)



Mounting

Make sure the motor and VFD are securely mounted. Use vibration-dampening pads or mounts between the motor/VFD and the floor or mounting surface. These pads will absorb vibrations and prevent them from transmitting to the building structure. Neoprene or rubber pads are common.

Enclosure

If practical, consider enclosing the motor in a sound-dampening enclosure. This can significantly reduce airborne noise. Use materials like mass-loaded vinyl (MLV) and acoustic foam. Be sure to provide adequate ventilation to prevent overheating.

Acoustic Barriers

Place acoustic barriers or panels around the motor and VFD to block sound waves.3.

VFD Carrier Frequency Optimization (Revisited)



Sweep

Don't just try one or two higher frequencies. Perform a sweep of carrier frequencies, starting relatively low (e.g., 2 kHz) and incrementing up to the maximum allowed by your VFD (e.g., 16 kHz or higher). Listen carefully at each step. There might be a frequency range where the noise is minimized.

Random Carrier Frequency

Some VFDs have a "random carrier frequency" or "spread spectrum" mode. This slightly varies the carrier frequency, which can help reduce tonal noise.4.

VFD Parameters and Filtering



Switching Frequency (Advanced)

Some VFDs allow you to set the switching frequency independently of the carrier frequency. This can sometimes help reduce noise.

dV/dt Filters

If you're using long motor cables, a dV/dt filter can help reduce voltage spikes that can contribute to motor noise.

Sine Wave Filters

Sine wave filters are the most effective at reducing motor noise, but they are also the most expensive.5.

Motor Examination



Bearings

Bad motor bearings are a common source of noise. Listen to the motor with a stethoscope. If you hear grinding or rumbling, the bearings likely need to be replaced.

Motor Mounting

Ensure the motor is correctly mounted and that all bolts are tightened to the correct torque specification.

Fan

Check the motor fan for damage or imbalance. A damaged fan can create significant noise.

Winding Inspection

If you suspect winding issues, have the motor inspected by a qualified motor repair shop.6.

Grounding



Verify Grounding

Ensure the VFD, motor, and any other equipment are properly grounded according to the manufacturer's instructions. Use a dedicated ground wire.

Ground Loops

Check for ground loops, which can create circulating currents and noise.7.

Load Analysis



Load Type

What is the motor driving? A pump, fan, compressor, etc.? Certain types of loads are more prone to vibration.

Load Balance

If the load is unbalanced (e.g., a pump with an impeller issue), it will cause the motor to vibrate.

Load Speed

Run motor at different speeds, does noise get worse or better?8.

VFD and Motor Compatibility



Motor Type

Is the motor suitable for use with a VFD? Some older motors may not be.

Motor Size

Is the motor properly sized for the load? An undersized motor will be working harder and may generate more noise.

Manufacturer Recommendations

Consult the VFD and motor manufacturer's documentation for compatibility information and recommended settings.

Important Considerations for the Apartment Above



Communication

Keep the residents of the apartment above informed of your troubleshooting efforts. Explain what you're doing and how you're trying to reduce the noise.

Timing

Schedule noisy troubleshooting steps (e.g., running the motor at different speeds) during times that are less disruptive to the residents.*

Professional Help

If you're unable to resolve the noise issue, consider hiring a qualified HVAC technician, electrician, or vibration analysis specialist.

In summary, the most effective initial steps to take are to isolate the source of the noise, use vibration-dampening mounts, and explore acoustic enclosure options. Then, systematically work through the other troubleshooting steps, starting with the simplest and most common causes. Flag for review