Speaking of that plastic cowling, I had a clicking noise that sounded like it was coming from the "A" pillar, passengers side by the windshield/dash area. This started 6 weeks after I bought my xB in Aug. 07, thought that it was the dreaded "A" pillar TSB fix that was needed, but I didn't want them taking my car a part and I just lived with it. Last night I read on another site where a person was having a clicking noise which was coming from the wiper cowl piece where it touches the windshield and the fix was to put some light lube under the cowl piece and let it soak down between the piece and the windshield.
I tried this last night and the clicking noise is gone! I am going to keep an eye/ear open to see if it returns, if it does, it 's an easy fix. I just sprayed the lube from the can lightly (used the red plastic straw) and let it soak behind the plastic.
I used white lube, you could probably use WD-40 or something along that line. Since you only use a little and it is at the bottom of the windshield you shouldn't have any problem with the lube going up on the windshield. Just wipe off what is left on the outside of the plastic.