Nissan xtrail diesel 2008 makes a whistling noise when going down hill and backing off replaced turbo still making nois

SOURCE: Loud whistling noise when travelling at higher speeds (ie above 50mph)

I had a problem with a whistling car after 50 mph and it turned out to be the front window gasket. I put silicone on the trim and problem solved.

SOURCE: Jeep grand cherokee 2.5 turbo diesel power loss

hi i have bean told it is the number 1 injector with the wire attached you might need it replaced thanks

SOURCE: model is 2ltd turbo diesel Whistling noise from

it could be a loose pipe on the turbo. the noise would get louder with higher revs as with higher revs higher boost is produced. check for loose pipes and give them a tighten then try a test drive. hope it helps you

SOURCE: 1999 Altima: My 1999 Nissan altima is making a loud whining noi...

you call it the serpentine belt, we call it the fanbelt.it,needs tightening,slightly loosen the alternator, then pull away from engine and tighten belt, tight enough when you can move longest part of the belt, between pulleys, 1/2 inch in/out.
if squeel re occurs fit new belt.

SOURCE: clutch makes whistle noise

Sounds like a throwout bearing is dry.