I uploaded some .wav files just to cut off the starts and ends of the audio. When I playback in audacity, it sounds just like the original file. However, after I export to .wav (48000 Hz, unsigned 8-bit PCM), there is a lot of fuzzy and grainy background noise that appears out of nowhere. This is version 3.7.4
That’s what low resolution (8-bits) sounds like! 
There is audible quantization noise in the background. It’s similar to regular analog noise in-that it’s most audible with quiet sounds and mostly drowned-out with louder sounds. But unlike analog noise it goes away completely with digital silence.
Or… it could be dither. Dither is (optional) intentionally-added noise that’s supposed to sound better than the “natural” quantization noise.