if you never heard the turbo wistle before,i would suspect an airleak post turbo,intake gasket,plenum bolts loose , hole in turbo to snorkel hose,etc.
check belt tensioner pulley for bad bearing.
98 GMC sierra 2500 ext cab 4x4 auto tr 6.5 td 252000 km. needs new engine, next project
95 GMC sierra LE 2500 ext cab sh box 4x4 auto tr 6.5 td 328.000 km. my wife's truck .remote pmd on cooler
89 GMC sierra SLE 1500 ext cab 4x4 auto tr 6.2 720000 km engine swap at 665000 km because of broken oil cooler line. 6 bolt wheels.
Waldon wheelloader repowered with a 6.2 na