Audi Idle Noises

[George Durden <durden@bga.com>]

My 88 Audi 90 makes a similar "knocking" noise only
on cold mornings at idle for about the first 60 seconds
of running. My mechanic thinks it is the hydraulic lifter(s)
loosing it's static pressure through a leeking check valve in 
one or more lifters. This causes a little slack in the cam lobe
to lifter connection and the resulting slapping or "knocking"
It's in the queue for further diagnosis and probable lifter
replacement in the spring...

A question for the Audi list:
Has anyone replaced/rebuilt the heater fan motor in a 90?
I'd be interested in your experiences and extrication
procedures... please email directly.

George