Apple said on Friday that it’s replacing AirPods Pro headphones that have sound problems.

These problems include a static or crackling sound that increases in loud environments and issues with active noise cancellation.

Apple said AirPod Pros made after October 2020 don’t have the issue.

Owners who experience problems can contact Apple online or make an appointment at an Apple store to get their AirPods Pro replaced for free. Only devices that are confirmed to have the issue will be replaced.

The replacement only applies to the buds, not the charging case. Apple’s not offering a similar program for other AirPod models.

Crackling problems with AirPod Pros were reported by users earlier this year. In May, Apple issued support documents on its website with troubleshooting advice for the issue. It was replacing those units under warranty.

Apple’s AirPods are a popular line of wireless headphones. Apple doesn’t break out revenue from AirPods, but it reported $7.8 billion in other products revenue in the quarter ending in September, which includes AirPods along with other headphones and the Apple Watch.