Buzz in Input 1 of Korg DTR-2000

[bthrem]

There's a distinct buzz in the Input 1 signal path (front and rear) of my Korg DTR-2000 when I plug in my P-bass and Jazz bass. It's not 60 Hz hum, more like single-coil pickup buzz. This buzz does not occur when I plug the basses into input 2 (rear) of the tuner. The buzz does not occur when I plug in active basses into Input 1.

Just curious if anybody knows what the difference may be between Input's 1 and 2 on the tuner. Thanks!