Pops and crackles is caused by juice hitting the coil to be vaporized. The sounds are perfectly normal although some juice delivery devices and/or juices are quieter than others.
You mentioned variable watts so I'm guessing that you have the new iTaste VV 3.0. If that is the case set it to the variable watts (VW) mode as that doesn't require any math or oHms knowledge:
iTaste VV V3.0 User Manual
Variable Wattage Mode :
Hold the + button first and then holding power button for two seconds to enter variable wattage mode. The digital screen will show the puff count first , then the last setting used (in voltage or wattage). Wattage can be adjusted from 6.0W to 11.0W in 0.5 watts increments by pressing the + and - button.
Start at 6 watts which is the lowest setting and use the + and - buttons to adjust the watts up or down to your taste preferences. The iTaste will automatically do the math to provide the same power if you change to a different juice delivery device with a different oHm rating.
Holding either the + button or the - button will cause the display to show puff count and current mode (VV or VW). In this state, you can also adjust the voltage or wattage by pressing the + button or -button.
As a general rule of thumb try starting fruits, sweets and tea flavors at about 6-7 watts and tobaccos or coffees at about 8-9 watts.
Use your own judgement about whether to switch or clean out your iClear 16 heads between flavors. Some flavors go well together and some combos can be downright disgusting.
To clean your iClear 16 remove the drip tip. Then take the iClear 16 apart by unscrewing it from the base and unscrewing the head which is the metal tube part that holds the coils and wicks. Pull off the white silicone tube above the wicks.
Rinse everything well with hot water being very careful that you don't wash the silicone tube down the drain.
Pat the silica wick as dry as possible with a paper towel. Be very gentle as the wicks are extremely delicate. Dry the other parts including the inside of the tube that holds the juice.
Screw the head back onto the base and the base back onto the tube that holds the juice being careful not to get the wicks caught in the threads.
Turn your iTaste to 6 watts and press the power button for about five seconds or a little more. At this point you are just burning off water. Keep a constant watch on the coils by looking down the the center tube. When you first see the either of the coils just start to glow orange begin using only half second pulses with the power button. Pause it least five seconds or ten seconds between pulses. Firing for too long once the coils start to glow can pop the coil which ruins it. Repeat until all the coils glow orange evenly.
Let things cool for a minute or so and remove the base. Blow any residual ash off the coils. Put the white silicone cap back on the head and screw the base back on the tube that holds the juice. Fill with juice and put the drip tip back on.
This process is called dry burning and will get rid of gunky juice built up on the coils that can reduce your coils ability to efficiently vaporize juice and, if the coils are dirty enough, can discolor juice and make it taste bad. How often it needs to be done depends on your juice and what your tolerance is for dirty coils. I clean after only running between 2 and 3 ml. of juice through my devices but I can't stand the taste of even slightly dirty coils. Most people clean much less frequently and some never do. They just toss dirty coils and replace with a new one.
Some juices will react very badly with your iClear 16's plastic tank,
juices that crack the plastic on clearomizers. Pick up a Kanger Pro Tank which has a pyrex tank to use with those juices. A mini version should be available soon that won't be so top-heavy on your iTaste.
