Choosing Wood For Maple Cap

[Crusader]

The Maple I bought for the cap (22 x 8 x 3/8") has been in the shed a few months now and is slightly warped and cupped (by about 1/8") - should I still use them?

I think as long as I can check they are actually flat when they're flat, I should be okay

What I'm planning is to screw them to something at the corners then sand them and check for flatness

But I'm also wondering about tap testing. I'm very familiar with doing this with fretboards or anything that I can grasp but these pieces are bigger than I can hold in one hand, so I drilled a little screw in each side at 1/4 length

Being quite wide it produces a different sound by tapping at the edges than the middle (all about an inch from the end)

Tapping close to the edge they produce close to the usual sound but tapping in the middle I get a confused "double" sort of sound (there's a term in Physics books for this but right now I can't think of it)

Basically they don't resonate for long

Could this indicate the timber has hairline cracks or something else undesirable?

[Crusader]

No-one got any suggestions about this?

I also have to add that I get this "double" sound when I play the sixth string on most of the guitars I've made

And when checking intonation on my guitars the tuner needle wanders up and down a lot - but with the SG it reached a point and held steady

I know if I lean forward the reading goes down and if I lean back it goes up and I'm quite sure its not buzzing on any frets or the nut or the bridge

So my thoughts go towards inferior timber, bad glue joints or poor installation of the bridge & tailpiece posts

Kind-of changed the subject now but anyone got any thoughts?

cheers