Yes.
http://www.industrialnoisecontrol.com/comparative-noise-examples.htm
Your brain learns to not focus on certain noises, so a PC fan at the same level may seem louder than the background noise.
Conversational speech is 60 dBA
My PC on on all the time, I actually find it harder to sleep with it off, it's too quiet.
Every 10 dBA is double the noise.
Damn, look at what hits 90. I remember back in 1998 at one of the motocross tracks on a KX125 someone clocked me with the soundgun at 97dBA.