Yes, there is a belt that drives the power steering pump. It goes from the crank sheave to the pump's sheave (pulley). Try tightening the adjustment on the pump or maybe (worse case) go to the parts house and get some belt dressing.
If it isn't a belt squealing, it could be internal noise. Mine does this sometimes on full turns at moderate speed (taxes the pump). I think a rebuild or replacement might be in order for mine in the near future.
Can anyone tell me what's involved in rebuilding an original '68 PS pump?
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'68 El Camino