If the sound quality is diminished, especially all of a sudden, try removing the instrument's wax guard. It is typically a white cap on the end of the device and can be removed with a tool or often with your fingernail. The device will function without the wax guard, so you do not need to be able to replace it immediately but you should eventually - within a few days - get another wax guard put on.
If your hearing instruments don't seem to be working correctly you can try:
No sound or intermittent function - change wax guard especially if sudden, with no other sound or low battery warning. If the aid has no wax guard or it has already been changed try a new battery ( you could also try the battery from the other aid if you are wearing two and the opposite one works).
Static noise with reduced function - moisture or debris in microphone needs clearing with brush tool.
Performance fades out - change battery.
Your best understanding in noisy conditions will be with sound perceived equally by the brain from both ears. If one ear is significantly louder than the other, the brain will only recognize information, regardless of where is is coming from, from the louder side. With normal hearing we are able to separate speech from noise, because we hear it equally loud to both ears and can then perform auditory figure vs. ground perception, i.e., separating the voice we want to hear from the noise. If sounds are not balanced, you cannot separate things well and it is much harder to understand conversation.