Fabia vrs Siren whistle

Yep, its one of them topics again.. now I know there is plenty of topics on this but there seems to be every answer possible all over the forum. now for the last few months the whistling has worsened, its the dreaded siren noise. although its only noticeable when in low revs, under 2.5k. could this mean its the turbo on the way out? even though its making the whistle whilst its not under boost. could this be a boost leak? the catalytic converter? intercooler? also theres no black smoke at all and seems to be no others signs of the turbo on its way out and also theyre doesn't seem to be any lack of power.

Any past experiences or thoughts?