Just had my engine rebuilt and its running great......but three weeks after I now get a whistle when the engine comes under load. If the revs are low or I am going down hill no problem no noise. As soon as the engine comes under load it starts and the noise follows the engine revs put your foot down and the sound increases with the revs. I took it back to the garage they stripped part down looking for air leaks and said the couldnt find any. Put it back together and....no noise...later that day it came back again. Any ideas other than shouting or turning the music up! Could it be the head gasket leaking or my turbo about to blow up?

How loud is the whistle , my turbo whistles as I accelerate, always has done

mine used to whistle
that could have been down to it having no cat, no silencers, no egr, a K&N and snorkel though
worth looking at the manifold and exhaust though as mine once made a noise a bit like blowing through a blade of grass, turned out one of the exhaust gaskets was blowing slightly

leaking intake or exhaust manifold

Hi Guys

It gets louder as I increase speed, loud enough to hear clearly inside and very loud when the drivers window is open.

Not turbo whistle then... I'd be hedging my bets intake or exhaust manifold too then

Thanks everyone for your input, I will take it back to hospital Monday with a list of things to check....great help thanks I will post the results. have a good weekend.