Our DS was, and sorry to say still is, a poor sleeper... With a not completely dissimilar routine to your DD at his age. I've seen other babies at toddler/baby groups who just magically go to sleep - our DS and I suspect your DD, just don't do this. If there is something to be interested in he will be interested in it - he needs no visual stimulation and no aural stimulation; so we use and still do use a quiet darkened room with radio 4 on.
However at about 8 months we had to send DS to nursery and get him down to a couple of day time naps to match their routine.
As you found with your DD if we tried to get DS to stay awake longer i.e. after eye rubbing/yawning starts then we just ended up with a really difficult settle/complete meltdown. So what we did was start to shorten the naps we wanted to get rid of by waking him before he would usually wake rather than letting him sleep - this meant he then slept longer at the other naps.
This may or may not work for you though...
However, by 8 months he was having 1 morning nap of 20-30 mins (in the car on the way to nursery on nursery days) an hour's nap after lunch and then another nap around 4-5pm (in the car on the way back from nursery). As he has got bigger he dropped the morning nap and then the early evening nap himself.
However - you're question was about solid facts on white noise/sun shades; I've got nothing on sun shades I'm afraid but noise I have done some research on in the past (for on-deck noise on aircraft carriers so not strictly relevant...) I've done a quick search now and this supports what I found last time:
Children's hearing and noise
Basically providing the white noise is well under 85dB then there should be no problem. Given that 60dB is normal conversation and 70dB is a vacuum cleaner I imagine you're well under that - if you're playing white noise over 85dB then I have to agree with the GPs :)