Trying to diagnose an odd whistle : 59 plate 1.8TFSI, 85000 miles. Doesn't tend to whistle in first. Whistle first appears in 2nd at 4800rpm, stays on to limiter appears in other gears, perhaps a little earlier. Its a fairly low pitch whistle. Its not what i'd call the normal turbo whistle if that makes sense. Im wondering if this has a boost bypass issue ?