Austarion

Im going to get it rebuilt, because I dont like the noise, but Im just curious as to what it actually is.

When the turbo spins up, it makes this loud brrrRRRRRRRRRRRR noise. It gets louder and the pitch changes the faster it spins. When I take my foot off the gas you can hear the turbo spinning down (gets quieter and pitch lowers).

Its definately the turbo, no doubt about it.

But whats actually going on inside the thing?

My first thought is a worn bearing/blade making it unbalanced??

A cracked exhaust manifold will also cause this sound.

Wouldn't a cracked exhaust manifold would change pitch/volume as soon as the throttle was released, or if the engine rpm dropped?

It takes a while for this noise to disappear, about 5 seconds 'BRRrrrrrrrr r r'. Kind of like a circular saw how you hear it spin up, run and then spin down - just not so loud and a slightly lower pitch. Its very steady and smooth.

Definately sounds like a bearing or misalignment or unbalanced blades. I had a cracked exhaust manifold and it only made noise when i was backing off throttle and it only made a very distinct exhaust sound.

Out of balance or maybe something scraping?

sounds like something is in the way of the airflow of the compressor or turbine, I had a noise like that in one of my amps at home, it turned out to be a wire had found its way in front of the fan blades, not touching but close enough to make a bfrrrrr noise as it wound up and down. there could be crap in front of the compressor, or the turbine....