First, determine what's making the squeaky noise (e.g. axle springs, ubolts, shackle bolts, bushings, bearings, etc.). If shackle bolts, bushings, or bearings, then tighten or replace hardware. Do not overtighten shackle bolts (see below for torque specs). If axle springs are culprit, jack trailer up to relieve springs, then use chain and cable spray lube. Lithium grease may also help. If the springs are damaged or failing, then replacing springs may be the only remedy.