Turbo noise V...V...V (like a police sirens)

Dear All: Recently my trooper (1996 Diesel Intercooler Turbo 3.1D) have big noise (V...V..)when I driving, The repairman told me it should a noise of the turbo bearing attrition, and he told me no one can repair the turbo inside because of the design. Whether I need to replace a whole set of it, or keep driving it is whether safe? Best Regards, Chan Wai Lun