Your problem is likely just related to the belt, not a bearing or tensioner. I have the exact same problem, and so do many others with older Whipples. You'll want to replace the belt but the problem will reappear if you don't address the actual problem. As Evan Guyett found, the Whipple pulley is about .100" rearward of the plane of the other pulleys -
http://www.fordgtforum.com/forums/showthread.php?23152-Whipple-Belt-Chirping-Explained-and-Corrected
And so a shim is needed. Whipple is (very) quietly handing these out to those who ask. What is happening is that your belt is rubbing against the aluminum face on the front edge of the pulley. The belt is now shiny and the anodizing is gone, creating a major noise. Evan suggests relieving the face to add some clearance. pe2unia's Ultra Grip Pulley has this feature as well but I fear he is not correcting for the offset problem. Theoretically if everything is aligned and the belt and pulley are the same width as OE, clearancing should not be necessary.
Certainly the idler should not be push too hard, as it is easy to bottom out the tensioner, which could add a lot more load to the rest of the set and cause further problems. The reduction in tension surely reduces the noise, but it will still return in time if the interference is not resolved (via the shim).
Given that Whipple is offering these shims, I suspect at some point recently (in the past year) they revised their units to address this. Only they know the serial number at which this occurred...