Your harmonic balancer has slipped. You need a new one before it disintegrates and spins the outer ring off and into something else. o.o The squeal is caused by the outer ring of the balancer spinning against the rubber/poly separator material in the balancer due to separation of the parts.
This is actually getting to be a common complaint from '00-'03 owners AFAIK
Owner of NPORA, mod for Nissan-Infiniti Forums, NissanForums.com, NissanHelp.com, AllNissans.com and VGPowered Forums
'88 Pathfinder: 6" of lift, 33x13.50 Swamper LTB's, Rancho 9000's, L&P Stage 3 steering system, K&N, Pacesetter headers and 2.5" exhaust, Lock-Right locker, 110A alty and electric fan swap, dual batteries, 700W+ worth of PIAAs, etc.