Hyundai Santa Fe intermittent noise

I have a 2009 automatic 4x4 Santa Fe. Since I purchased three months ago I have an intermittent problem which only shows when the car has been used a lot during the day (such as when the engine is warm) - rarely when used for just a short run. Obviously this makes it very difficult for the garage to diagnose the problem. They have changed the turbo and unfortunately the noise is still coming and going. The noise is like a rubbing high pitched noise which can get quite loud and is most obvious in low gear such as commencing climbing a hill. However it can be heard sometimes on the straight roads. Any suggestions?