JJ getting checkraised on flop 100NL

[jacknine]

Shorthanded 100NL game. 4 players at the table. Been there for about 20 mins.

SB ($208.00) Hardly seen him play any hands since I sat down so I´d assume he´s quite tight.
BB ($134.50) Has beat me into one pot where he called a 4x BB raise with J9o and rivered 2 pair against my TT.
UTG ($233.00) Know him to be a loose player
Hero ($93.00) Not played much apart from my TT.

Preflop: Hero is Button with J[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/club.gif[/img].
<font color="#666666">1 folds</font>, <font color="#CC3333">Hero raises to $4.50</font>, SB calls, BB calls.

Flop: ($13.50) 9[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/diamond.gif[/img], 4[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, BB checks, <font color="#CC3333">Hero bets $15</font>, <font color="#CC3333">SB raises to $45</font>, BB folds, Hero...

I thought I was ahead on the flop so made the bet there to take it down. After the check-raise, I´m not so sure anymore.
What is the BB holding here? And - if he is holding a hand that beats me here, would he really make this type of move?