Check the belt tensioner...mine was swapped out while the car was in the shop for the leaky timing chain cover...engine sounded noisy then, too.
Much quieter now.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car