Android 5.1.1 update is rolling out to the NVIDIA Shield Tablet, with the OTA coming in at 767MB. According to the release notes, the update brings stability and performance improvements, along with system-wide optimizations and audio fixes.
Earlier this year, a few users found that the speaker on the Shield Tablet was acting abnormally, emitting a screeching noise when loading certain games. This update hopefully fixes those issues.
Source: Android Central