Troubleshoot the noise by using spray silicon
e or belt dressing. With the enginer off, use the spray attachment and apply a small amount of fluid behind the pulley onto the shaft bearing area. Begin with the alternator, spray it, start the engine, check for the noise then move onto the next component (e.g. power steering, a/c, etc).
Basically, the component that briefly stops making noise is the component that is suspect, Turn off the engine, remove the belt and verify the tolerance on the pulley of the suspected component. Use both hands and pull/push vertically on the pulley assembly. If you get more than 1/8" slack then I would say you most likely have a bearing failure and you should replace that component.
Good luck and let us know how you make out.