I'm hearing a constant hissing noise through my Sennheiser headphones. How do Sennheiser users solve it?

Make sure the volume on your headphones and the device you're connected to isn't too high. Excessive volume can occasionally result in distortion or noise.

Make sure the headphone wire is securely connected to both your headphones and your device. Loose connections might result in interference.

Check for any evident damage to the headphone cable. If you notice any cuts, bends, or frayed wires, these could be the cause of the hissing noise.

Connect your headphones to another device or audio source to determine if the hissing continues.

Electronic equipment such as cell phones, Wi-Fi routers, and microwaves can occasionally interfere with audio signals. Try moving your headphones away from these gadgets to see if the hissing stops.

These tips are what we can offer, if you know more or better ones, please share.