5kTQ Noises

["L. Scott Oliver" <SOLIVER@gcwf.com>]

Quattroheads:
Any assistance with two disturbing new noises would be deeply
appreciated.  Car is an 87 5kTQ with 140k miles.  In driving from LA to
San Francisco yesterday it began making two new noises:  First: it
sounded normal when at a steady speed, but if I applied even a tiny
amount of throttle, I could hear a faint buzzing, almost like a cricket, from
the engine.  I thought it was pinging or piston slap at first, but the
symptons don't fit either.  It can only be heard on very quiet roads, and is
now present any time I accelerate (though it's most noticeable by far in
4th and 5th gear).  It vanishes if I let off the throttle or push in the clutch,
and can't be detected when I open the hood while stopped.  No known
exhaust leaks, previously or now, and no obvious torn CV boots or
leaking parts.  Number two (related?): if I let off the gas entirely and stay
in gear (coasting to a stop), I hear (at high speed) a clanking/ringing
sound from the drivetrain, which at lower speed becomes a clunk/clank
sound from the region of the trans, center diff, or prop shaft.  Again, it
vanishes if I push in the clutch, and can't be detected when the car's
stopped.  Any thoughts, experience, or guesses?  I'm praying it's not
expensive...

TIA!

--Scott