Need help solving engine knock

Hey, I have a Toyota Hilux diesel truck. It came with the 3l 2.8 ltr engine but had a turbo fitted to it.

So recently I was driving and dropped it to 2nd gear from 3rd and all of a sudden I hear a metal noise which wasn't too loud and afterwards the engine started to overboost (it's set to 1 bar and now its overboosting to like 1.5 bar) and it's also doing a knocking sound which gets worse with higher rpm. Truck didn't lose any power after this happened.

Can anyone help me what to look for?

Thanks

The overboost condition makes me think you broke something with your wastegate so now it's flopping around and making the knocking noise. 

Don't diesels run by knocking?  

I am confused by the question.

More boost than what you have fuel for can cause a lean condition that can cause issues.

I'd be checking the turbo setup and see why it's overboosting.

Something wrong with the exhaust?

Edit: the overboost could have also caused a rod knock.  Also, Do you still have oil pressure?

In reply to wvumtnbkr :

Compression ignition isn't knocking, even though the reasons are similar. There is kind of a knock effect for diesel, kind of a super fast combustion. 
 

But I think many of the other ideas suggested are a better path to go down. It's not normal to have a runaway event, which could also be an oil leak in the intake system. More fuel burning gives more boost and more forced oil in system to burn. 

Diesels are always lean, unless you are rolling coal, so I wouldn't spend too much time on that just yet. 

Can you hear the knock at idle?

If so, I would start by slowly loosening each injector line one at a time until the RPMs drop and listen to see if the knock goes away then retighten the line. If the knock goes away then you know which cylinder is knocking. Once you know that, I would swap the injector from the cylinder that's knocking with one from a different cylinder.

Once you do that, repeat the process of loosening the lines one at a time until you find the knocking one again. If the same cylinder is knocking after swapping injectors then it's internal to the engine or the injector pump. If it follows the injector then you have a bad injector, and just meet to replace it.

If the injector is sticking it may not be atomizing the fuel, causing that cylinder to not burn correctly and dump excess fuel into the exhaust causing the higher boost