Is it a dentist drill type of noise? If you're sure its the turbo you need to get it out of there asap, as it wears all that metal is circulating in yout oil if the turbo goes it flings all kinds of crap down the oil return into the engine. Or if the oil seal goes you could run out of oil in seconds. Just replaced an engine where the turbo went, piece of the shaft was in the sump. You can pick them up on ebay reasonably enough both new and used.
