Roar at 2800rpm

[Jlkguitars]

I recently had a problem with the pulley driving the power steering and the alternator. It had to be towed to a local mechanic and he replaced the pulley and ever since I get this weird noise that 3 local mechanics can't figure out and one if them wants to rebuild the engine. I am convinced this is not going to resolve it. One of them thought it was the turbo and sent it to be serviced which improved the power but the noise is still their. On cold start up she will rev up and not make this noise but as she warms up it growls as you hit 2800rpm and then goes away after 2900rpm, this happens in any gear and is louder the harder you accelerate. It isn't loosing power, I have had them check all the plastic around the fan etc but this isn't the problem either. I am going to send it for a transmission service as its due anyway and one if them has suggested it may be the viscose fan or perhaps a fan clutch relay. Has anyone had this problem or have any idea of what it may be. I do a lot of miles and its driving me mad not to mention causing heads to turn it is that loud.