How to Quiet a Noisy Air Conditioner

If your AC noise feels like a hum or vibration traveling through walls or floors, the issue is likely structure-borne. In this case, the goal is to isolate the unit from the surface it sits on using isolation pads or a heavy-duty isolation mount to significantly reduce vibration transfer.

This approach is simple and effective, especially for units mounted on brackets or placed on rigid surfaces like concrete pads. It won’t reduce airborne noise much, but it can dramatically cut down on low-frequency rumble inside your home.

Step 1: Map out Fence Placement

Start by positioning your barrier as close to the AC unit as possible without obstructing its ability to operate. The fence should be at least 1.5 to 2 times taller than the unit and extend 3–4 times beyond it on each exposed side. Alternatively, you can fully enclose the unit, using your home as the fourth wall.

Step 2: Build the Fence or Mounting Structure

Construct an airtight barrier using dense materials like wood, brick, or concrete. If you plan to hang blankets instead, build a sturdy frame that allows you to secure materials tightly at both the top and bottom using the pre-installed grommets. For more detailed instructions, see how to build a soundproof fence.

Step 3: Add Soundproofing Material (Optional)

If your fence is lightweight, reinforce it with sound blocking materials. You can hang mass loaded vinyl outdoors or you can hang Quiet Quilt™ Outdoor Soundproof Blankets. If you used wood, brick, concrete or a similarly heavy material with zero gaps, then adding a material with mass won’t make a huge difference.

Step 4: Add Absorption (Optional)

If you used sturdy materials like wood, brick, or MLV, add absorption to reduce reflected noise. BlocknZorbe (charcoal version for outdoor durability) is ideal.

If you used soundproof blankets, this step is not necessary since they have an absorptive facing. You can also browse our outdoor sound blankets for alternative configurations.

If reducing noise at the source isn’t enough, the next step is preventing it from entering your home.

For unit noise, focus on sealing and upgrading nearby windows. There are multiple ways to soundproof a window, including inserts like Fantastic Frame Soundproof Window Inserts. You can also review the amount soundproofing a window costs before starting.

For HVAC-related noise, address the ductwork. Learning how to soundproof your ductwork can reduce noise traveling through vents. We also have a how-to article for soundproofing an HVAC closet or even broader strategies like soundproofing a wall or how to soundproof a room.

In many cases, the best results come from combining multiple approaches. For example, isolating the unit can eliminate vibration noise, while adding a barrier reduces airborne sound, and window or duct treatments prevent remaining noise from entering your home. By layering these solutions, you can target different noise paths and achieve more noticeable overall reduction.