Sansui au555 integrated...white noise help please.

Picked up a Minter that sounds superb and works flawlessly but my only moan is a steady white noise in quiet passages or between tracks which the Fostex drivers reveal ruthlessly.The amp is stock original and after some googling it appears that this could be a case of some noisy transistors in the preamp section?I was hoping someone here could offer some wisdom.....really love the build and quality of this amp circa 1969.Smooth and warm almost untransistorlike sound. ;DThanks in advance.