Diesel knock when fuel level is low

[AidanKildare]

Hi,

I’ve a Verso with the 2.0 D4D engine and approx 180,000 miles. When the fuel level drops to the second last bar on the fuel gauge, the engine has a distinct diesel knock on acceleration which goes away if I refill the fuel tank. I’ve fitted a Toyota fuel filter and added an injector cleaner to the fuel but the issue is still the same. The old fuel filter was clean and didn’t have any water in it. 
 

Has anyone had the same issue or suggest what might be causing the knock? 

[Perfection]

Could it be the fuel pump noise? 

[AidanKildare]

16 hours ago, Perfection said:

Could it be the fuel pump noise? 

That's something that I hadn't thought of.  I'll see if I can recreate it with the car on the driveway and see if I can track down the location of the noise.  It's usually apparent under load