I'm hearing some strange noises - squealing, or thunder/hissing noises.
If you're hearing really weird noises from your stethoscope, that possibly change when you press on the diaphragm, there's probably some lint or foreign speck of dust inside your stethoscope. Fortunately, One is super-easy to clean. Refer to the Cleaning Instructions regarding unscrewing the diaphragm and using a dry air spray to clean out the space around the sensor.
While rare, we occasionally see this problem. The origin of such noises is quite simple. There's a high voltage between the diaphragm and the plate behind it. This is the unique Thinklabs sensor design. If a piece of lint gets into your stethoscope, it might sit between the high voltage plate and some other part of the circuit, or the diaphragm. The lint then provides a current path for the sensor to discharge. This tiny pico-amp or nano-amp current flow will sound like thunder or strange sound effects after it's amplified, but in reality, it's completely benign in terms of potential for damage. So don't worry, just clean it out.