The felt paper is for a moisture barrier; NOT for squeeks! Squeeks can be caused from loose nails that no longer hold the sub-floor to the joists. If you're working over concrete, a crawlspace, or an unheated basement, it's best to keep any moisture out. The moisture comes from the warm floor mixing with whatever is cold, especially the air, below it. This 'meeting' creates condensation, and obviously, a wet floor will get ruined. DON'T go putting down any type of padding under you floor. If you DON'T follow the directions, you could void your warranty. Contact the mfgr on the WEB and tell them the type of room you have below the unfinished floor, and what you have for 'layers' on your floor no (w/o the finished floor.) The directions you might be reading are probably for installation above a heated room (like a 2nd floor bedroom over the kitchen.)
Before you install your floor, locate the squeeks. Use deck screws (that will go 3/4" into your joists) to hold your subfloor to your joists. Or shim from below if possible. My best to ya and hope this helps.