From my EXP thus far...
PlayStation 3 Phat - Very quiet 90% of the time, but if you play to long are doing some really iffy things they needs more of the cells power then it gets as loud as a fridge.
Xbox 360 - Really loud when playing games straight off the disc, i don't have a big hard-drive yet so it does get pretty iffy, but it doesn't effect gameplay, i just make the Vol louder.
Wii - Not much from what i see, i played it a few good times at my uncles and its as quiet as a PS2.
PSP (2000 Model AKA my FAVE) - Easy going most of the time until it loads a big ass area or something, then it makes this weird as almost spooky sctrachy noise.
DSLite / DSi - Not sure, i haven't officially choosen one yet so don't have an opinion on this one...
PS3 Slim - Dunno.
