Mbox line level input noise using keyboard

[egraham]

Wondering if anyone else has experienced this. When I hook up a keyboard to the Mbox I notice a subtle amount of steady white noise coming from my keyboard (Roland XP-50). Unfortunately this gets recorded to track. One track with the noise is bearable, but after recording mulitple keyboard tracks the noise stacks on top of itself. To a slightly discerning ear this is unacceptable. I feel that the noise levels when using a mic input are very acceptable and multiple tracks with a mic input doesn't cause this problem. I have tried a different Roland keyboard and found the same problem. I should try another brand of keyboard and see if the problem still persists.

Here is what I have done to try and remedy the problem:
-Made sure the output levels from the keyboard were set at their maximum
-Tried multiple types of cables including Monster 100 & 500
-Tried a couple different brands of DI box (even though I know a DI box shouldn't be necessary)

None of this seems to help. If anyone has any suggestions they would be greatly appreciated. Not sure that this is pertinent to my problem, but I'm running PT LE 6.1.2 on an iMac G4.