Intermitent squeal-ish problem.

Usually, if there is an end play problem on the crank, you'll also hear the problem in neutral when you rev the engine. The crank will move back and forth when you raise and lower the RPM. I guess it's possible that with the added strain of being gear could move the crank just a fraction more and cause the flex plate bolts to clip the bell housing dust shield but I wouldn't think that would make a sound like he's describing. It only takes a minute to check so why not? The more things you eliminate, the closer you will be to finding the problem. When it makes the noise, is it continuous or does it pulse or vary or go louder/faster with engine RPM?