A) This is not Insignia.
This is FixYa.com a Product Support website.
B) This recent post of yours is in the Free section, and looking back at your problem you posted, it is in the Free section also.
C) The website does have a Premium section where problems are charged a fee.
You're not in that section.
Shall we go on, and delve with your volume control on your sub-woofer?
The Volume Control on your sub-woofer is a Potentiometer. A variable resistor in this case.http://en.wikipedia.org/wiki/Potentiometer
Observe the top photo, then go to the illustration below it.
(You can click on the photos/illustrations, and enlarge them. You can enlarge twice)
The construction of a Potentiometer varies in it's usage, and by the manufacturer.
(I doubt Insignia makes their volume controls. They buy from a manufacturer that does)
Your volume control won't look like the second illustration down, but it gives an illustration to show you to help explain the following;
See the triangular shaped piece that extends from the shaft in the middle? Number 3
This is the Wiper Arm.
Note the round shape that the Wiper Arm will slide against. The circular outside portion.
The circular outside portion is a Resistor. There is a contact on one end of the circular shape, and a contact on the other end of the circular shape. (Or a contact on either end of the Resistor)
With the Wiper Arm at one side of the Resistor, no volume is allowed out. As the Wiper Arm is slid across the Resistor, more volume is allowed to come out. When the Wiper Arm is at the other end of the Resistor, there is no resistance, and you have full volume.
With a volume control you are not turning the volume up.
The volume is already at full blast. When you turn the volume control you are allowing more of the volume.
It could be compared to having a garden hose in your hand, the water is already on full blast, and you have the hose pinched off with your fingers.
The more you let go of the hose, the more water comes out.
The popping sound you hear is a dirty contact between the Wiper Arm, and the Resistor. A few spots on the Resistors surface, actually.
OR, there is a worn off surface on the contact end of the Wiper Arm.
Would mean the volume control would have to be accessed.
For dirty contacts:
You could try removing the volume control KNOB, and using the plastic straw provided, use an electronic cleaner. (Spray can)
Squirt the cleaner down in the volume control, then turn the shaft back, and forth.
If this doesn't do it then the volume control would have to be replaced.