Always clean your thinkfab and make sure everything is tight and secure. You should develop some type of schedule to care for your thinkfab depending on your usage. I clean and check each day and on Fridays I oil the rods and lube the blower fan if needing, ( I have one fan that needs a tiny half drop of oil once a week). Be sure to keep an eye on the screws used to tighten the heating plate. I try to check these every time I level the bed.

From this point it will be assumed that the Nozzle is free and clear, working. That the feeder tubing is in good shape, and clear and working from the nozzle back to the feeder. Your are able to print, just not getting good results and hearing a strange noise or two.

Now the basic symptoms. If you are hearing:

1. A "Popping" sound or loud "click or Clicking". The duration of this sound runs from just once to several time all very fast.

2. A grinding noise, lasting 2-3 seconds, sometime longer, like a gear is slipping.

Possible cause and solutions:

Issue #1. The Popping noise. Usually cause by filament slipping in the filament feeder as the gear is trying to push the line forward. Normal response is to tighten the nob, applying a small amount of pressure back on the filament wheel. This usually works, but it is also a hit or miss. Often is very hard to find the balance of not to tight and not to loose, but just right.

Recommend replacing the tension spring used on the filament feeder. You will still have to learn how to apply the right pressure but a new spring usually clears up the "Popping" noise I have found. You can also switch springs from the other feeder to check and see if a new spring will help. Know that to much pressure is not always a good thing either.

Issue #2. The grinding noise. The exact cause officially is still to be determined. Many think it is caused when the filament is  retracted. So far I am of the belief that all to often this is not the cause.  In my opinion it is often caused by "Back Pressure" from the nozzle. Causing the filament to slip backwards because it was moving forward toward the nozzle and for various possibilities was not able to do so. Like a log jam, pressure builds up and the result is the grinding noise from the gear inside the feeder. Each time this occurs some of the filament is shaved off, leaving small amounts of plastic. This needs to be cleared or it will act like a lubricant, adding more slipping.

As of this writing I personally can offer only a few basic solutions:

Make sure that the feeder is clean, filament line is clean, clear of dust, dirt, oil, grease and anything else. Try not to handle your filament as much as possible. Wear cloth gloves if possible.

Level the build plate:
This does take time to learn but worth it. The more you do it the easier it is and you can get a better feel for your prints and see the results. 

Check your Nozzle Gap:
Distance from the build plate to the nozzle is recommend to to start at 0.3mm, when using a 0.4mm nozzle. Recommendation, purchase a simple feeler gauge, use the 0.3mm gauge to set you thinkfab nozzle gap. This is close to the average business card. Mankati recommends using a business card. I DO NOT! Get a feeler gauge if you want better prints. I have recommend to Manakti to include a feeler gauge finger, the 0.3mm in each parts kit that comes with the XT. I believe by doing so thinkfab would see a decrease in simple printing issues posted here cause by poor "Nozzle Gapping" by using a business card. 

Measure your Filament:
If you have a caliper, measure you filament, see if it has the right tolerance to move inside the tubbing. 2.95 with a + or - of .5 is shaving it close. I try to buy filament that has a slightly better tolerance, 2.85 with a + or - of .05.

The above has help me to reduced to all most zero grinding or slipping. If you are still having issues with grinding then contact thinkfab support, see if there is anything else that can be done.