My A4 has developed a new noise. On boost and on load there's an odd constant tone. The tone changes when I come off the throttle and goes completely. If I just rev the engine it sounds completely normal. But on load as the boost comes in this tone appears. It's not the DV noise as its constant on load. The car has had the DPF and EGR removed with new pipes and been mapped to suit but not too aggressive. One question, if the EGR cooler pipe has been blanked off wwould that cause back pressure on the turbo vanes? Another small issue is that on a long drive last week the low oil light came on so I stopped at a Halfords and bought some Halfords own brand 5w30. Although it is a 170 it no longer has the DPF so I thought the oil would be ok. I only put in about a litre. Not sure if that has anything to do with it. As an aside it's still using coolant too. Not much but it is going somwwhere. Bit fed up now. It's almost every week a new issue appears. Might put back to standard and get rid.