Like HotI said as long as the click isn't hurting, it's fine and can be quite 'normal'. DD occassionally clicks when the let down is too fast & like Barb said, she coughs & splutters. I sit her upright, give her a few seconds and reattach her. DD also started feeding more frequently during the day, more late arvo, early evening (say 1.5 - 2 hrs) and as a result she sleeps longer at night. The past two nights she has only woken once for a feed overnight & it was a long feed, like 25 mins all up with a quick nappy change (usually feeds are 10-15 mins).
Keep an eye on the nappies, wet & dirty are a good sign. Your baby will become more alert as he gets older so the milk drunk look might not happen as often now.