RRC 200tdi help please.

[TheGolfGuy]

I have a Range Rover Classic with a 200tdi engine converted from a v8 a fair few years ago - previous owners. The knocking appears to be coming from the intake/exhaust side. It is present from idle. Strangely, if I cover the air filter housing inlet by hand, the engine still runs but the knocking disappears. I did try covering up this inlet. The engine ran but the turbo & intercooler pipes were constricting as engine speed increased (using throttle cable on top of injection pump).

I tried removing the air filter housing completely incase it was a turbulence issue within the housing, however, the knocking persisted. Does anyone have any guidance on what to check or what could be at fault?