Is it a large project to remove the headliner and check to see if the drain tube has come loose from my sunroof assembly?

That is nearly impossible to do at home

They go down inside front A pillar an inside rear D pillar . To get at them you need to take trim off an the headliner down .
Sunroof Housing Rear Drain Hose Replacement (Impala)
Remove the headliner. Refer to Headlining Trim Panel Replacement in Interior Trim. Remove the rear quarter lower trim panel. Refer to Rear Quarter Lower Trim Panel Replacement in Interior Trim. Disconnect the rear sunroof drain hose from the sunroof module rear spigot. Remove the tape from the rear sunroof drain hose tube.
Disconnect the rear sunroof drain hose from the rear sunroof drain hose tube. Remove the rear sunroof drain hose tube from the upper retainer clip. Remove the rear sunroof drain hose from the rear pillar
The front is simalier .

YOU HAVE TO REMOVE THE HEADLINER THER IS 4 TUBES ONE IN EACH CORNER MAKE SHURE THE TUBES ARE CONNECTED TIGHT BEFORE YOU PUT THE HEADLINER BACK

The drain tubes should be located on the four corners of the factory sunroof assembly, running down the four windshield pillars.

Check for any obstruction in the rail.

Also, can check this procedure to test your components...
Power Sunroof - REMOVAL & INSTALLATION (click over pic for zoom)

Motor
See Figure 1

1. Remove the sunroof switch panel by pushing it to the side and disengaging the pawl, then pulling it downward.

Fig. 1: The sunroof switch panel is retained by a metal clip

1. Remove the sunroof switch bracket.
2. Unplug the sunroof motor wiring harness connectors.
3. Remove the sunroof motor mounting screws.
   

Disassembly of the sunroof motor is not recommended.

To install:

1. Lightly lubricate the drive gear with grease and install the sunroof motor to the sunroof assembly.
2. Plug in the electrical harness connectors to the sunroof motor.
3. Operate the sunroof to verify proper operation.
4. Install the sunroof switch bracket and the sunroof switch panel.
   

Sunroof
See Figures 2 and 3



Fig. 2: Exploded view of the sunroof assembly on 1993-94 vehicles



Fig. 3: Exploded view of the sunroof assembly on 1995-97 vehicles-1998 models similar

1. Tilt up the sunroof lid.
2. Remove the lid side trim.
3. Remove the lid bolts and the lid assembly.
4. Remove the rear drain mount screws and the drain.
5. Remove the shade assembly holders from the sunroof frame.
6. Remove the shade assembly.
7. Remove the sunroof switch, interior accessories and headliner.
8. Remove the switch bracket.
9. Remove the motor assembly, spacer and clip.
10. Remove the wind deflector mount holders from the sunroof frame.
11. Remove the wind deflector.
12. Disconnect the drain hose.
13. Remove the sunroof brackets.
14. Remove the sunroof frame assembly.
15. Remove the link and wire assemblies.
    

To install:

1. Tilt up the sunroof lid.
2. Install the link and wire assemblies.
3. Install the sunroof frame assembly.
4. Install the sunroof brackets.
5. Connect the drain hose.
6. Install the wind deflector.
7. Install the wind deflector mount holders on the sunroof frame.
8. Install the motor assembly, spacer and clip.
9. Install the switch bracket.
10. Install the sunroof switch, interior accessories and headliner.
11. Install the shade assembly.
12. Install the shade assembly holders on the sunroof frame.
13. Install the rear drain mount screws and the drain.
14. Install the lid bolts and the lid assembly.
15. Install the lid side trim.

Hope helps (remember rated this help).

The motor is located in the recess above the near side wheel arch and is mounted on a small frame held in place by two 10mm bolts. In order to remove the motor you will need first to extract the sunroof cable that runs though it. What follows sounds complicated but is quite quick and easy. 1) Ease the sun roof back to half open, if the motor is not working just put a 17mm socket on the nut in the centre of the motor and hand crank it open. 2) Between the sliding metal roof and the headlining panel, about 10cm from the leading edge, are 4 pop connectors. Slip a large bladed screw driver between these and separate. 3) Ease the headlining panel forward and pull it up and out through the sunroof aperture. 4) Now close the sun roof, if necessary using the same hand crank method used to open it. 5) On the under side of the sliding roof panel at the rear in the middle you will see the end of the cable tube guide . Mounted at the end there is a metal butterfly mount located with two 8mm bolts. This mount is what actually holds the end of the cable to the sunroof bridge mechanism. Remove these two bolts and withdraw the whole cable forwards, again the hand crank can help here. Take care this cable will be filthy. Check the end for signs of teeth missing - if so replace and clean the motor gear box of metal shavings 6) Returning to motor - disconnect the electrical connector block. 7) To the front of the motor the sunroof cable tube is held in place with a clip. Push the tube end at 90 degrees to the motor body towards the outside skin of the car to un-clip and to disengage it. 8) to the rear of the motor you will see a similar exit cable tube. This time the the tube must be pulled at 90 degrees to the motor towards the car interior and when unclipped this needs to be moved away towards the rear to clear the motor assembly. 9) Once the two 10mm frame mounting bolts are removed the motor can be extracted 10) Check the health of the (replacement) motor gear box by removing the three 8mm bolts holding the steel backing plate in place. The large plastic driven cog can be removed by undoing the 17mm nut on the other side whilst holding the central spindle with a 6mm open spanner to stop it rotating. 11) Clean everything to a shine and re-grease liberally. 12) Reassembly is the reverse of the above remembering to clean the drive cable and re-greasing prior to reinstallation

There is a drain tube from the sunroof that may be loose or broken, and leaking into the vehicle.

You will have to remove the headliner to access the tube and check it.

The rear window may have a bad seal as well - allowing water to seep in.

In either case - the headliner must be removed to pinpoint the leak.

Thanks for using FixYa - a Very Helpful rating is appreciated for answering your FREE question.

should be at corner of sunroof assbly have to drop headliner to get to them

You have to remove the interior trim panels to allow you to pull down the corners of the headliner. Once you can see the sunroof track you will be able to see where the drains attach and hook them back up.

chances are the tube has come off of the sunroof assembly. remove the headliner and check for the problem