Troubleshooting and Fixing a Noisy Mini-Split Compressor

A noisy compressor in a mini-split system can be a significant issue, causing discomfort and disrupting daily activities. The primary sources of noise in mini-split systems are the compressor, fan, and refrigerant lines. To address a noisy compressor, consider the following steps:

Vibration Isolators

Replacing conventional mounting bolts with vibration-damping connectors, such as those from McMaster Carr, can effectively minimize vibration-induced noise. These vibration isolators work by absorbing the mechanical vibrations generated by the compressor, preventing them from being transmitted to the surrounding structure.

When selecting vibration isolators, consider the following factors:

  1. Load Capacity: Choose isolators with a load capacity that can support the weight of the outdoor unit. Typically, mini-split outdoor units range from 50 to 150 pounds, so select isolators accordingly.
  2. Vibration Frequency: Identify the dominant vibration frequency of the compressor, which is usually between 10 to 30 Hz. Select isolators with a natural frequency well below the compressor’s vibration frequency to ensure effective damping.
  3. Deflection: Opt for isolators that provide a minimum of 0.25 inches of static deflection to effectively absorb low-frequency vibrations.
  4. Material: High-quality rubber or spring-based isolators are preferred, as they offer superior vibration-damping properties compared to basic rubber mounts.

To install the vibration isolators, follow the manufacturer’s instructions carefully, ensuring proper alignment and tightening of the connections.

Spring Mounts

mini split noisy compressorImage source: Flickr

In addition to vibration isolators, utilizing spring mounts can further dampen low-frequency noise, especially if standard rubber mounts prove ineffective. Spring mounts work by providing a more robust and adjustable vibration-damping solution.

When selecting spring mounts, consider the following:

  1. Load Capacity: Ensure the spring mounts can support the weight of the outdoor unit, typically ranging from 50 to 150 pounds for mini-split systems.
  2. Spring Rate: Choose spring mounts with a spring rate that matches the natural frequency of the compressor, typically between 10 to 30 Hz.
  3. Adjustability: Opt for spring mounts with adjustable features, such as leveling bolts or pre-compressed springs, to fine-tune the vibration damping.
  4. Stability: Select spring mounts with a sturdy base and anti-vibration pads to prevent lateral movement and further reduce noise transmission.

To install the spring mounts, follow the manufacturer’s instructions carefully, ensuring proper leveling and adjustment of the springs to achieve optimal vibration damping.

High-Density Rubber Foam

Placing a double strip of high-density rubber foam behind the outdoor unit can help reduce vibration and noise. The rubber foam acts as a barrier, absorbing the vibrations generated by the compressor and preventing them from being transmitted to the surrounding structure.

When selecting high-density rubber foam, consider the following:

  1. Thickness: Opt for a minimum thickness of 1/2 inch to effectively dampen vibrations.
  2. Density: Choose a high-density foam, typically with a density of 4 to 6 pounds per cubic foot, to provide sufficient damping.
  3. Compression Resistance: Select a foam with a high compression resistance to withstand the weight of the outdoor unit without significant deformation.
  4. Adhesive: Use a high-quality adhesive, such as a construction-grade polyurethane or acrylic-based adhesive, to ensure a secure bond between the foam and the mounting surface.

To install the high-density rubber foam, clean the mounting surface, apply the adhesive, and firmly press the foam into place, ensuring a continuous and even coverage behind the outdoor unit.

Regular Inspections

Regularly inspecting the mini-split system for loose components or foreign objects that may cause rattling noises is crucial. Over time, vibrations and environmental factors can cause components to become loose, leading to unwanted noise.

During the inspection, pay close attention to the following:

  1. Compressor Mounting: Ensure the compressor is securely mounted and that the mounting bolts or brackets are tight.
  2. Fan Assembly: Check the fan blades for any signs of damage or imbalance, and ensure the fan is properly secured.
  3. Refrigerant Lines: Inspect the refrigerant lines for any loose connections, clamps, or insulation that may be causing rattling.
  4. Outdoor Unit Mounting: Verify that the outdoor unit is firmly secured to the wall or mounting bracket, with no signs of looseness or movement.
  5. Foreign Objects: Carefully inspect the interior and exterior of the unit for any foreign objects, such as debris or tools, that may have been left behind during installation or maintenance.

If any loose components or foreign objects are identified, address them promptly to eliminate the source of the noise.

Proper Installation

Ensuring the mini-split system is installed correctly, with adequate space around the outdoor unit and proper bracket mounting, is crucial for minimizing noise.

When installing the mini-split system, consider the following:

  1. Outdoor Unit Placement: Locate the outdoor unit in a well-ventilated area, away from obstructions and with sufficient clearance around the unit to allow for proper airflow.
  2. Mounting Bracket: Ensure the outdoor unit is securely mounted on a sturdy bracket that is properly anchored to the wall or ground, preventing any movement or vibration.
  3. Refrigerant Line Routing: Carefully route the refrigerant lines, avoiding sharp bends or kinks that can create turbulence and noise.
  4. Insulation: Properly insulate the refrigerant lines to prevent condensation and reduce the transmission of vibrations.
  5. Electrical Connections: Verify that all electrical connections are tight and properly grounded to prevent any electrical interference or buzzing noises.

If the noise persists despite these measures, it is recommended to consult a professional HVAC technician for a thorough inspection and potential repair or replacement of the faulty components.


Addressing a noisy compressor in a mini-split system requires a systematic approach, focusing on vibration isolation, spring mounts, high-density rubber foam, regular inspections, and proper installation. By implementing these strategies, you can effectively reduce the noise and restore the quiet operation of your mini-split system.

Remember, if the noise is persistent and excessive, it is always best to consult a professional HVAC technician to ensure the issue is properly diagnosed and resolved.


  1. GreenBuildingAdvisor – Help! My Minisplits Make Tons of Noise
  2. Cool Power LLC – 5 Common Mini-Split Noises and What They Mean
  3. Reddit – Mini split owners: do your indoor units make extremely loud noises on a regular basis?
  4. YouTube – Why is my Mini Split So Loud?
  5. HVAC-Talk – Lennox Mini-Split (MLA009S4S-1P) Indoor Unit (MWMA009S4) Making Strange Fan Noise