Cordless vacuum makes loud high-pitched whistling noise during use

Safety first: Remove the battery before inspection.

• Localize the noise: Run the vacuum briefly and listen around the bin, hose joints, and filter cover to find the source (then switch off and remove battery).
• Check bin seal: Inspect the rubber gasket around the dust bin. Clean dust from it and the mating surface. Replace if torn or hardened.
• Inspect hose: Flex the hose and look for splits. Replace if any cracks are found.
• Ensure covers are fully closed: Press firmly on the filter cover and bin until they click.