My friend who installed RBs ran into the same problem and asked me the same question. The dilemma is that you want to wait for as long as possible to save money in the long run, but also you do not want to end up having blown turbos causing damage to other parts of the engine. I also wish someone had a method of determining where the sweet spot is.
I am at 60,000km and don't hear any turbo whine under normal use or regular WOT. But I can hear the turbos "after" spin right after having done a donut or otherwise going from WOT to "silent" very quickly. Like if I do WOT in 1st or 2nd and then let off the throttle very quickly and listen carefully. I guess the sound is always there if the turbos are spinning, and that it is getting worse over time, but is usually just buried in other noises. It's not really a whine on mine yet, but definitely a spinning noise. My DCT also whines a bit at certain rpms when very hot but that is a completely different topic, and something I have just learned to ignore.
What mileage is your car at?
What target boost/tune are you running?
Do the drivers of your car have a habit of ignoring the oil temp gauge because the car is under ext warranty / leased?
I mean do you usually warm up for 30-60s before driving off, and wait to do spirited driving until the oil temp gauge needle has started moving? Or do you live at the bottom of a mountain and the only way to town is going WOT uphill with a cold engine tuned to 20psi?
