Ok, this morning when i was driving to the garage to have the oil/filter change done, the turbo or something in the engine sounded like a police siren noise. when it was warm the noise disappeared. i didnt intend to use the turbo when it was cold but needed to get away quickly. however, whats foxes me is there is no smoke whatsoever coming out of the exhaust.

is this a sign of imminent failure or just cause it was cold.

my car is coming up to 70k on the original non recond turbo