Since its quick to do I gave it a try yesterday - removing the foam (C2S).

Put the foam back.

No difference. My decibel meter confirms that.
Very slight bias towards higher frequencies with foam removed.

The rear panel has a plastic protrusion on the right side that goes over the sound symposer orrifice. This is intended to provide clearance of the foam at that location (the foam should not block the hole) - make sure that is the case.
The foam itself is accoustic and has the effect of increasing the virtual volume of the chamber formed by the panel and the rear. Similar to what happens in a hifi speaker. This lowers the resonance frequency of that space. That's a good thing...

Rainier

Thanks Rainier!


Was wondering if anyone can take a couple of quick phone pic and post it here on what to look for and what the sound symposer looks like. That would really be appreciated!

I'll be checking to make sure my sound symposer is not blocked when I pick up my car.

The difference is not huge, but I do find that there is a difference ONLY on heavy throttle though. If you leave the cover off entirely, the is even a bigger difference, but the sound is somewhat hollow without the cover (if that makes any sense). Sure wish my car would sound deeper and throatier on idle and normal driving and not have to push hard on the gas to get the engine to sing.