Apart from the usual chugging diesel noise, the car makes two loud noises. At low revs, it gives a gruff deep sound. This reduces drastically if much higher revs are applied. On motorways, l have to press the accelerator right to the floor to avoid a horrible deep sound, instead l get a less horrible higher pitched sound. On motorways or regular roads, when l take my foot off the accelerator (or release the pressure on it) it takes a long time for the noise to drop in pitch. l would like to identify the problem and fix it or at least find ways to deaden the sound a bit... l can not hear my stereo!

something with the turbo perhaps?

Have the pump checked.

Try to isolate where the noise is coming from - is it the engine or the drive train? Does it change pitch when you put your clutch in? Does it vary with road speed? Do you still get the noise if you put the car in neutral when you are rolling along the road etc? Is it worse on acceleration or deceleration or turning in one direction? Is it something on the accessory drive belt - alternator, pulley etc?