Why would a turbo on an 1994 Isuzu trooper make a squealing nosie?
If it's not the regular turbo scream from the high rpm turbine
it might be the blades hitting the housing and the shaft bushing in
the turbo might be worn out. Take off the in going air hose on the
turbo, the one that comes from the filter. You can now get to the
end of the shaft in side the turbo and feel for play by pulling
gently up and down. There shouldn't be much play. If it gets really
bad a turbo blade can break and get sucked in to the engine. Not a
lot of fun. Have the turbo rebuild before it gets too noisy.