GIANT CSR 3.0 SQUEAKY BOTTOM BRACKET

I bought (2nd hand from a reliable first owner) a GIANT CSR 3.0 hybrid / light tourer that I use for commuting to work and back (approx. 18m / 1200’ascent / descent).
I’ve got a horrible squeaky noise coming from the vicinity of the bottom bracket. I’ve recently fitted shimano spd / flat combo pedals so they are O.K. and I can’t feel any slop in the crank spindle. I’ve also fitted a new chain (to late – as it jumps a bit) but can’t see this contributing to the problem as it was there before change. It’s my first aluminium framed bike and if it’s as stiff as it is suppossed to be could a BB on the limit of wear be responsible. Any advice sought brfore I try the local cycle man.

P.S. Nice bike otherwise – shame it’s not in steel.