"Our almost 16 week-old baby seems to want to be held or be resting next to me while he sleeps. If I try to put him down or leave his side, he wakes up. Even if we hold him while he's sleeping, he still wakes up at about 25 to 35 minutes into sleeping, and has to be helped back to sleep again by rocking or nursing. I would love to be able to put him down and have him sleep for even just an hour. It seemed like we were able to do so weeks ago and I'm not sure why this is happening. He does sleep well at night, waking every 2 to 4.5 hours to nurse, falling back to sleep again nursing, between about 7-8 p.m. and 7-8 a.m. Am I expecting too much at this age for his napping? He also startles very easily and wakes from small noises in the house -- the cats, a dish clinking, a paper rustling. Should I be making it louder to "condition" him to sleep through noise, or putting him somewhere even quieter? Thank you!"

- Jenna, Berkeley

Depending on the amount of sleep your baby is getting, which isn't entirely clear from your post, he may indeed be a bit sleep deprived.  Requiring being held, awakening frequently, needing contact with you in order to stay asleep are often associated with inadequate sleep.
 
Of course, needing contact to fall asleep isn't unusual, but when babies can only remain asleep when they are being held, that's a possible sign they're not getting enough sleep. 
 
In addition, the being very sensitive to noises may also be a sign of inadequate sleep.  This usually though not always gets better once your baby starts getting enough sleep.  My advice is not to focus your attention on modifying the baby's sleep environment.  My advice would be to focus on his inner rhythms as described in the book. 
 
Did you receive the book yet, did reading the book offer any possible solutions or new strategies for you?  If so, have you given them a try?   Let me know when you can.