A tranny noise that concerns me

[fngearhead]

So, I finished my EJ20G swap last summer. The engine and tranny are 1989 JDM. Lately the tranny has begun making a whirring noise while coasting. Its not all the time, just anytime there is no real load on the drivetrain. If I'm on the throttle accelerating or hard engine braking, everything sounds normal. Its kind of in that grey area between accel/decel. No noise when the clutch is disengaged. It seems to be very slowly getting louder over the past month or so. This engine/tranny apparently had only 68k miles on it when I installed it. Can't say I'm excited to take it apart again.