A4 engine whistle (not turbo)

[Douglas Frank]

Car is a '98 A4tqm.

I sometimes hear a trilling whistle from the engine while passing
through 3000-3200 RPM.  It happens both accelerating up and
coasting back down in gear.  It almost, but not quite, goes away
as the engine warms, and the affected RPM range narrows to 3100
or so.

Any ideas?  (As I said, this happens only sometimes-- for
instance, it didn't happen this morning, after a cold night).

Oh, I had an, um, incident a year ago and there's a wobble in the
engine-driven fan's viscous coupler, left over from having the
rad pushed into the fan.

thanks!
--
Douglas Frank Compaq Computer Corp.  Lead, n.  A metal, useful as
ZKO           110 Spit Brook Rd.      counterpoise to an argument
603-884-0501  Nashua, NH USA 03062    otherwise unanswerable.