Imma start a Grateful Dead cover band and call it the Noodles. Oh wait... someone already did that!
I never worked with the Dead, but my sound company and I did lots of shows with the Jerry Garcia Band. Once the load in was done, Jerry would more often than not plug in, sit on a road case or something, and just noodle away while we were finishing setting up the stage and patching up the sound system. He was always experimenting with different approaches to playing a riff, and seeing what might work here and there, etc. I can't say I never heard him noodle during a sound check too, or sometimes, occasionally, even during a show a little. I never gave it a second thought at the time, and neither did anybody else, I'm sure. Whatever Jerry wanted to do was fine.
In and around 1965 Jerry was teaching guitar at Dana Morgan Music in Palo Alto, California, and playing in a band called the Warlocks, which is a story in itself. The guitar lesson was you would strum out a rhythm guitar part Jerry would show you, and Jerry would noodle around trying this and that on lead while you were providing back up. From time to time Jerry would then pick up the rhythm part, and if you were paying attention to what he was doing, you could attempt to play what he had just done. Then he would jump in there and you knew it was time to strum some more so he could essentially continue practicing his riffs, etc. That was the guitar lesson, with a certain other aspect thrown in there as well! Quite a learning experience!
Dana Morgan had an old couch in his music shop up against the wall just as you walked in on the right side of the joint, and between lessons or if he didn't have anything booked for an hour or so Jerry could usually be found on the couch back then noodling away on his guitar through one of the rental amps on the floor. So if nobody else was already doing it, you would plug in and play rhythm guitar parts Jerry would ask for over and over again till your fingers got numb, while Jerry noodled away working on his chops.
I would say from my menial perspective that with just a few exceptions, the only times I ever saw Jerry beginning from Dana Morgan Music and going forward was when he was playing his guitar. Somehow, whatever Jerry did always seemed okay. Now, if
you start noodling in between songs or on stage before a show, that
might be a different story.