buddy's burb is possessed...

[jb1016]

...well, maybe not possessed, but it is making a weird noise that we can't pinpoint. 93 burb, 2wd 350, silverado pkg, yes, I've posted for this guy before. Noise happens after he starts it up, and when he shuts it off. It's a clicking or tapping - like a fan hitting something - but when it quits, after 15 seconds or so, it doesn't trail off, it just stops cold. The speed interval of the noise changes. It seems to be coming from the passenger side footwell, under the dash. It's independent of the a/c - he's tried it with the air, and the fan, both on and off, and it does it no matter what. It's got us . Any help is welcome and appreciated.