I have a tapping that comes from the headrest. It sounds like metal on plastic...like the headrest connecting bars are tapping on some part in the seatback. Is this the noise you're talking about? If so, I'd love some ideas to fix this.
The common squeeking noises usually come from the seat belt latch area....i think you have to fix those with pieces of felt or something to prevent the plastics from rubbing and hitting each other.

Matt
94 e320