Passat or jetta TDI chirping in cold weather and cold start- how to solve
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Introduction

If your 1996 1997 b4 Passat or 1996-1999 a3 Jetta has developed a chirping sound on cold starts in cold weather but goes away once the car warms up, a few things may be happening.  First check the following:

• If you hear a rubbing sound, first check the timing belt by unclipping the timing belt cover and looking for damage to the timing belt.
• Alternator bearings and pulley, power steering pulley, air conditioner clutch could be bad and creating noise.  The Jetta has a one way clutch on the alternator pulley which can wear out and create noise, the Passat does not.
• Accessory belt tension - as a rough rule of thumb to measure tension, push the belt at it's midpoint by hand, it should deflect about 1/2".  Warning: a tighter belt is not better because excess tension will destroy bearings and pulleys.  The accessory/serpentine belt on the TDI is automatically tensioned by a lever and spring.
• Oil, grease, or other fluids dripping onto the belts causing belt slip
• You can check the serpentine (accessory) belt tensioner pulley, clean and lube as outlined here.  I would just replace them with the harmonic balancer as described below since it's probably the cause, replacing the tensioner only can just temporarily fix the problem.

If these are okay, your car's harmonic balancer pulley and serpentine pulley tensioner spring may be worn out.  Replacing both of these will normally solve the chirping noise.  Summary of procedure: remove the belts and put on a new pulley and tensioning spring.  Grease the old tensioning lever or put in a new one.  Detailed steps below.

The noise is caused by inconsistent belt tension in cold temperatures.  The redesigned replacement harmonic balancer pulley should help reduce this tendency.  A large source of the drag that causes the noise comes from the alternator.  When you start the car, the alternator generates more load to recharge the drain of the battery from starting the engine and the glow plugs.  The cold temperatures may also cause the belts and the rubber parts of the pulley to contract and loosen.  Once the engine warms up the noise goes away.  If the engine doesn't make this noise once it's warmed up then this is most likely the source of the noise.

You can also disable the daytime running lights and reducing electrical load as a temporary way to reduce the likelihood of chirping.  Turning off the DRL will reduce the load on the alternator until the car is warmed up.  Once the car is warmed up, turn the headlights back on for safety.  For specifics on this procedure, refer to : 1000q: passat - disable DRL.  Also try turning off the radio, vent fan, or any other electrical loads.

Here is a picture comparing the old VW part #028 105 243K and the new VW part #028 105 243T harmonic balancer/dampener pulley/crankshaft pulley.  The old pulley consists of an inner pulley and outer pulley with a rubber ring in the middle.  When cold, the pulley contracts and slips, causing noise.  The new pulley is one piece with the rubber built into the ring.  Note the drilled dimple on the new pulley for balancing the assembly.

Parts (click links to compare current prices)

Harmonic balancer/dampener pulley #028 105 243T from tdiparts , from worldimpex, from AutohauzAZ, part #028105243T 
Serpentine belt (alternator) spring tensioner #028 903 315 R from tdiparts , from worldimpex, (worldimpex generic part)
new belts
4 allen bolts for the harmonic balancer (6mm) VW # N 903 487 04 (optional but suggested since they will probably be damaged during removal)
Relay roller #028 145 278 E (optional, it's the plastic pulley)
Protective Cap #028 145 291 A (optional)
Tensioning Lever #028 903 308 G (optional but not suggested)
Tensioning lever dust cap #028 903 310 (optional x2 pieces)

13mm socket
16mm socket
6mm and 5mm allen wrench/socket
T-25 torx screwdriver
PB Blaster (suggested)
High temp moly or all purpose auto grease
EZ out stripped allen bolt remover (suggested)

Procedure

Jack up the front of the car, chock the rear wheels, put the car in gear, set the parking brake on, set the car securely on jack stands on stable, solid, and level ground.  Make sure the car is secure before doing anything else.  Always wear eye protection, follow the precautions in the factory service manual, see the TOS for the full legal disclaimer.  Use a service cover or some towels taped to the fender to avoid paint damage from watches or belt buckles.  

Remove the plastic lower engine bay cover (T-25 torx and a few screws or bolts)

Spray a little PB Blaster on the 4x 6mm allen bolts on the harmonic balancer pulley.  They tend to get stuck and the PB blaster needs time to work.

Remove the power steering/water pump v-belt (outer belt).  Loosen the 3 red circled bolts (2 x 13mm), (1 x 16mm).  You can then swing the power steering bracket/pump a little to remove the v-belt.

Remove the serpentine belt by relieving the pressure off the belt.  You can use a wrench on the tensioning lever arm to move it while you slip off the belt.  Keep your fingers clear of the belt and lever in case it slips!  Although the service manual says to use the idler pulley's bolt, I don't do this because it can strip the bolt.  I also avoid using a screwdriver since it can damage the plastic pulley.  Then remove the tensioner spring (2 x 6mm allen bolts), (1 x 5mm allen bolt) marked by the 3 red circles below.

Here is another view of the lever and tensioner with the injection pump and bracket removed.

Remove the tensioner spring.  It's pressed onto the end of the lever, so I suggest using a lever to pry the end with the idler pulley to the pass side.  This will pop the tensioner spring off (pictured at about life size below).  Make sure the center allen bolt is removed.

Remove the allen bolts on the harmonic balancer pulley (4 x 6mm).  The bolts can be soft, so you may want to get replacements ahead of time.  Don't use the center 19mm bolt to counterhold the allen bolts because that bolt is attached to the crank!  It is a 1 use only stretch bolt and tightening or loosening it could lead to engine damage!  To counterhold the 4 allen bolts, I suggest putting the car in gear and having someone step on the brakes.

Suggested: spray the allen bolts with PB Blaster and let them soak to help loosen them.  Pictured below are the belts and the pulley removed.  While you are here, inspect the condition of the pulleys and other belts for oil or water leaks.  The 4 allen bolts will probably be hard to remove, I suggest having an EZ out (pictured above) handy incase the allen heads get stripped.  When using an EZ out, press on the bolt head and make sure it's sharp.  If you let it slip it won't bite into the bolt head and it will dull.

Installation is the reverse of removal.  Note: because of 1 offset hole, the harmonic balancer bolt holes will only line up 1 way!  I also suggest pulling back the tensioning lever boots and greasing the lever while moving it in and out, up and down.  If you want to replace the lever, see the steps below.  You may want to use a tiny touch of anti-seize on the 6mm allen bolts for the harmonic balancer so they won't be stuck next time.  The 6mm allen bolts come with threadlocker on them when new, so it's up to you whether to use any anti-seize.  I believe that they have threadlocker due to the vibration of a diesel engine.  However, I chose to use a tiny touch of anti-seize since the problem is more likely seized and stripped bolts and they were all tight when I removed them for another service.

Optional: Remove the tensioner rod by removing the airbox.  This is what it looks like removed, the advantage is that you can grease the whole rod.  The disadvantage is that it may not be necessary as long as you grease the ends and move it back and forth to spread the grease.  If you do, inspect the bushings for the lever for damage.  It's possible that a neglected squeaking can damage the bushings and this fix may not solve the squeaking.

If you remove the airbox, check for wires that have been rubbing through.  Clean the old grease off with brake cleaner or degreaser and regrease.  Keep the grease off the belt and pulley.

Put the new pulley on and reinstall the belts.  

Torque specs

Double check the torque of the four harmonic balancer bolts. (15 ft lbs).  The idler pulley bolt on the tensioner lever arm is also 15 ft lbs.

To tension the power steering v-belt, torque the splined tension adjuster (the bolt with the star spacer on it) to 2.9 ft-lbs for used v-belts, 5.1 ft lbs for new v-belts and then torque it's bolt to 18 ft-lbs.  The v-belt should have about 5mm of deflection in the middle.

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