I have an American Standard 2001 with Bi-flex truss. I've recently changed gauge from 11-52 to 9-42, so I can do Richard Thompson style double stops and wild bends. However, when I have .10 of relief, the truss rattles in the middle of the neck. The only way to make the rattling stop is to straighten the neck to about .05. But this is too straight for my liking and I don't like the feel and get some buzz on the first 5 frets with the neck that straight.
Could this just possibly be the spot between tightening and loosening the truss rod where they can rattle?

try a nut properly cut nut. I'm guessing you have a factory nut still on it, sounds like it's cut a little deep.

Its the nut?

bring it on over, hard to tell from here. From what you described, it might be the nut. I've never heard a truss rod rattle in the neck though. Still, from what you described, I would start by looking at the nut.

try .15 relief and adjust you action to taste and report back

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Guitars:
1. mid 70's Ventura MIJ Gibson l6-s clone (Pre-lawsuit) in Black with Rosewood FB and EMG 81 BR/ 85 Neck
2. ESP KH2 Neck Thru
3. 2008 Am Std Strat in 3 tone sunburst

You've gone anticlockwise of the center null point, I take it?

It's very unusual for a truss rod to rattle on those guitars. The biflex is a enclosed box unit. If it is the rod rattling, then it's likely broke. No amount of adjusting the nut will affect neck relief in that circumatance. So I'd rule it out.

I don't see how the nut would cause a neck rattle to appear so quickly. Nut slots wear in time with the frets in my experience. Very unusual on a bedded in guitar of a certain age. However I wouldn't say thats a wrong assessment, I'd just like it explained a little. Everyone could do with learning from everyone elses experiences.

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No no and no

I've experienced this phenomenon many times. Usually it is cause by both rods being at their 'neutral' points where one rod isn't compressing against the other and so, they tend to rattle in their respective channels.

As primitive as this may seem, I've found that a few fist blows along the back of the neck repositions the rods to where not only does the rattling go away but the neck needs to be adjusted again and so, the problem is doubly eradicated. YMMV.

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You dig?