96 850crackling sound behind headlight

Hello all

I have a 1996 850 with 150,000. There is a crackling sort of sound, just loud enough to be heard above the idling motor. The sound comes from directly behind the passenger side headlight and it usually will happen evn if I switch the key into the on position WITHOUT starting the engine. It rattles on for a few minutes and then fades out.

Any ideas?

Thanks in advance.