noise problems with C1 and new preamp

[tokyofan]

I've been running a new Grace 101 into an Mbox with a TLM 103 mic. No problems so far. But I just tried my Studio Projects C1 and when I power up I get a rather loud, constant hum that increases with gain. But when I plug the C1 directly into the Mbox, no noise at all. Any ideas? Didn't have any problems with the TLM 103. Please help!