I'll answer that after telling you how stupid I feel.
I took it on a hard highway run and then really got my head in there to listen to where the sound was really coming from. It was indeed the bleeder valve. If I pushed down hard on it, the sound stopped. Each of the bolts was able to be snugged up almost a full turn.
Good lord, this is why I never became a mechanic. I panic too easily.
Thank you all again, very much, and those that mentioned bleeder valve get the prize!
Now I'll go test it some more, and if it comes back I'll just replace the bleeder altogether.