[QUOTE=Frodo;259389]
The noise I'm trying to track down sounds a little like a few dice being gently rattled in a Yahtzee cup. Unlike his, I only notice it when starting to accelerate in 1st, then again accelerating in 2nd. It’s not there at idle, nor if the engine is revved but not under load. It’s subtle, but can be heard clearly when the engine access panel is removed. I removed the belt and the noise disappeared, even when accelerating in 1st and 2nd.
How can the sound be a loose spark plug if the noise goes away when you remove the accessory belt and run the engine?
Check the belt pulley & tensioner bearings for play (up & down movement) and also (if you have a manual transmission car) the alternator clutch which is mounted inside the alternator pulley itself. These clutches can grumble (like mine did) or chirp if siezed. It can be removed from the alternator shaft with a special tool. Steptronic cars don't have these clutches fitted.....