OSU 09 -
A squeal is usually related to the belt or a fluid flow of the hydraulic system.
Belt noise maybe more of a chirp and may change with engine rpm and/or turning or incline.
Hydraulic noise can also change with engine rpm, turning or incline but usually has a steady sound to it. The sound is consistent and the pitch of the noise changes to the load onto the hydraulic system.
It is best to visit the dealer to have this noise identified for a proper repair.
-The Toro Company