Your problem sounds exactly like what I was saying when I had a bad timing belt tension adjuster. This is not necessarily replaced when the timing belt is replaced (as it was not when I had mine done). Have you had a shop listen to it? You might just bring it by the place that would do the work in case something is wrong with it, and see what they think. I had to suggest a worn out TBTA before the shop guy said that it was probably a worn out TBTA. I replaced it, no more diesel. Abnormal noises are never okay.