Using the 2nd turbo on mine has been a serious metrological event . I needed some extra speed joining the M-way the other week and was surprised ( this is after a good few months of it not going above 2500rpm) to see a clear view of the road behind me. A few weeks later and a few more1000 miles and I tried it again nothing in the rear view mirror. The only thing that's changed is I had the intake doughnut replaced. I'd bought a used one and cleaned it out so I (the garage in the end) could do a quick swop when they were replacing a leaky injector pipe well before Xmas.  2012 TDV8 Vogue (L322)

Thats good news for you, on mine, there was no mistaking it, after just 20 miles or so around town using the loud pedal resulted in a smoke screen that James Bond would have been impressed with. Turbo crain mod done by Green Oval (great company) resulted in no more smoke screens, I didnt believe it would work but it did, perfectly. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6