Does it sound like this? Sorry, just couldn't help myself, but at least your thread got a bump back to the top.
Fan hub (clutch) engagement (slippage), fan drive belt slippage on fan engagement, belt tensioner or idler, or clutch slippage from momentary over torque to the driveline.
Check the four bolts that hold the turbo to the manifold, mine did that too, one was broke the other was loose. The one is really hard to see and that's how I missed mine.