So the daughter comes home, and says the 98 v70 has a knocking or tapping from the dash by the ac/heat/radio. Sure enough, I go out start it up and it is tapping/knocking like some kind of Morse code. Sound still is present when fan is off, but car needs to be running. Anyway what are your guesses heater core? a/c?

 

Play with the controls and see if it stops at a different setting. I am guessing one of the motors are stripped for the controls.

 

tech; does not go away when I change settings on dash.

 

How about with recirc?

 

I got the same thing happening with my 98 volvo s70. let me know what you find.