screaching is normally the turbo gasket just before as previously said it blows the gasket out and sounds like a tractor lol
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Try nipping up the 4 nuts up before she blows with a 13mm spanner
The nuts normally come loose because when the turbo has been changed the washers with tabs are not refitted before the nuts . ( they have tabs on them that bend down round the nut to stop the nuts coming loose)