I had been playing for about 20 minutes at my local casino, 2/3NL $300 max buy in.  I had about $400 in front of me.  I had one previous hand with villain.  I had 99, raised from EP and got called by villain.  I flopped a set and got 3 streets of value.  I think he called down with top pair because when I flipped over my hand he said “I can beat a pair of nines.”  Then the dealer told him I had a set and he said, “oh, a SET of nines.  No I can't beat that.”

Villain had been very active, playing about 70-80% of hands, raising with about 40%.  I had seen him raise PF with 43o in EP and other trash hands.  After the flop I would see him call a lot and lead out a lot if no one had bet, but I hadn't seen him reraise anyone yet.

I picked up the AQ in the BB.  Villain opened for $13, Button called, and I 3bet to $31.  Villain called and the button folded.  (it's really tough to range him at this point, I think he could have anything)

Pot: $77

Flop:  QT3

I lead out for $35 and villain calls.  He had been calling people down very light, so I was of the state of mind that this was exactly the situation that I had been looking for.  I thought he might have some kind of draw or maybe a pair.  Any pair.

Pot: $147

Turn:  7

I lead out for $55, and right after I put my chips out villain says “All in.”  Very quickly.  I hadn't seen him raise before.  At this point I am confused and I don't know what he could have.  I have about $300 behind, and I don't know if I should call or fold.

Thank you for your replies!