GU Whistle

This is a follow up to Thread 56399 started by Pepper 2. My 2005 3 Litre Diesel has developed a whistle which I can only detect at low speed. Pepper 2, how loud was the whistle in your engine and at what speed? Motor has only 42,000kms on the clock (owned since new) and the last couple of trips on the open road seems to have lacked power and would not kickdown when driving at 80 kmh. Recent service by ARB found nothing wrong, I did not mention whistle just that it would not kickdown.