Outer Limits 4x4 Board

i got a mq ute with the sd33 turbo motor & when it comes on boost i get a fast rattling sound from 1700 rpm to about 2200rpm kind of like a big end bearing but not as bad , i can only just hear it when i rev it up to boost without driving but when driving and under load its loud but when it gets high up into the revs the sound goes away, im thinking maybe a big end bearing or turbo problem , ive checked the obvious like fan ,alternator ect, motor has good oil & plenty of oil pressure its on 7psi boost and has just over 400000 on it so i guess its due for a few engine noises any help would be appreciated thanks

disconnect the wast gate and try it or pull off the intake pipe on the turbo and check the free play in the shaft.

i would say one of your injectors is getting stuck open mate.
its a very similar sound to a big end knock.

best way to check this is start your motor and bring it up to the revs where u can hear it knocking and then crack each injector one by one and if the knock goes away when u crack a certain injector you have found your problem.

1700rpm is where the fuel pump will start flowing more fuel and higher pressure.

give this a go and report back!