Thrust bearings are bearings that locate the crank shaft longitudinally in the engine block. These bearings can sometimes wear out and as a result cause noise. This is most common with vehicles with manual transmissions. The pressure exerted on the crank shaft during clutch operation is what causes the bearings to wear. Many times you will hear a noise when you depress the clutch pedal if you have worn thrust bearings. You might also see movement of the crank pulley when activating the clutch if the bearings are worn. That being the case, have a buddy observe the crank pulley as you apply the clutch. If you see movement of the crank pulley during clutch operation it’s very likely you have an issue with your thrust bearings. Here’s a video for you.