Used to get it on our ERJ-145's but can't remember when I last smelt it. Was a 'smelly socks' type smell. Bleed air comes from one of two stages depending on power setting and it may have been present as air changed over from one stage to the other. It is fixable and has been as like I said it doesn't seem to happen now, but was very common at one time.
Never affected me anyway (I think!)