Does this sound like a timing belt issue or IAB valve?

[SVX JAZZ]

When at idle (after my engine has warmed up) my engine has a slight vibration. This is mainly while at stoplights when the car is sitting in "D". It is not that bad but it is enought to rattle the stuff in my door handles (I put my sun glasses or cell phone there sometimes) or it causes a slight rattle in the plastic pieces in my interior. It doesn't matter if my AC is on either. Could my timing belt be a "cog off" or is my IAB (Idle Air Bypass) valve dirty? The car runs well and performs normal in all other ways.

Thanks for the help