If you've been good about changing the oil and oil filter every 3000 miles, you shouldn't have to worry to much about the chain yet. Most of them we see in the shop last about 150K. I would recommend replacement then or before if it does decide to start rattling. One of the biggest problems on the diesel though is chain stretch which throws the timing off enough to kill the power output and fuel economy.
ASE Master Technician, Lead Technician for Deutsch American Inc. Over 6 years of Import experience-specializing in German Automobiles.