Whenever I slightly adjust the "Channel Volume"

Hi, you hadnt mentioned how long you've had the amp, or how new it is, so I'm going to assume it's new to you. The Crate VTX200 has 3 channels, each with its own volume level. Let's check the simple things first:
1. Check to make sure you're adjusting the same volume knob volume knob to the same channel. The active channel will be lit with a green light.
2. Check the cables from the "Speaker Out" jacks on the amp (if you are using them). Are they plugged in all the way, or are they damaged?
3. Are you playing through a preset that you may have accidentally made "low", and may not be aware of or are stuck in it?
If none of these answers helps, there might be a problem with the input buffer in the circuit or possibly within the damping circuit of the speakers. I'd advise having the amp serviced to confirm an internal electrical problem also. If you don't have a manual for the amp, one can be found here:
http://www.manualguru.com/crate-amplifiers/vtx200/users-manual

1. Turn the main and monitor volumes all the way down (off). Plug a cd player into channel 9/10 and play a track of music of your liking. With the main/monitor volumes still off, adjust the gain on 9/10 until the clip light turns on, then back it down until the clip light just turns off. Put the channel volume at 12 o' clock.
2. With the music still playing, turn up the mains to the desired listening level first, and then adjust the graphic eq until the music sounds good in the room. Remember or mark the position of the volume control. Do not use the channel eq on 9/10 for music that has been mastered properly, leave the eq flat. Once this step is completed then you have now set the main eq.
3. Repeat the same for monitors. Turn off the main volume and then bring up the monitor main volume to the desired level first, then set eq. Now your monitor eq is set properly. Remember or mark the position of the monitor volume.
4. Set up microphone - plug a mic into channel 1 with volume all the way down. Speak or sing into the microphone and adjust the GAIN until you see the clip light, then back down a litttle on the gain. Put the monitor and main volumes back up to the mark from step 2. Now adjust the volume and monitor send on the mic channel to the desired loudness first before adjusting the mic channel eq. Use subtractive eq method to minimize distortion and feedback. ...i.e. if the mic is bassy then turn down the lows, do not ADD highs. If the mic needs bass, turn down the highs.

"Overdrive Channel: high frequency noise as the gain and volume are increased."

This is the expected result, you are experiencing feedback. Try turning the "Contour" knob all the way to the left and turn down the tone knob on your guitar.

In order to help you we would need the make and model of the mixer.

For the Drive channel you need to use the Drive control AND the MASTER volume control. When the Drive channel is active, the Channel Indicator lamp should be RED indicating the Drive Channel is active. The Drive control knob is used to adjust the preamp volume and distortion level of the Drive Channel. This gives you a clue as to what to check if adjusting the controls doesn't work -- the preamp tubes. Having said that, ONLY try to check these tubes with the amp OFF! Never stick your hand up into the chassis of a live amp. It could be lethal. Your preamp tubes are the ones farthest from where the power cord enters the chassis. They have a rubber like stabilizer on them. They have a tendency to wiggle loose, which is part of the reason for the stabilizer. Again, if you're not familiar with the insides...stay out and get an amp tech to help you.

The Normal Channel only uses the Volume Control to adjust volume.

In the first place you CANNOT connect your guitar directely to the snake ! You must use a DI box to convert the unbalanced output of the Baggs to balanced (differential) drive to the snake using either XLR or TRS cable. The DI should be driven as a HIGH impedance in and using "ground lift".

If the pots are noisy, lube sparingly with CRC 226 available in the electrical dept of Home Depot in a spray can with spout for about $2.70. Spray using the spout into the side where the leads go into the pot.

The volume pot is overly sensitive because you are overdriving the mixer at the other end. The trim on that channel of the mixer probably has to be reduced as well.

It sounds like your volume control is dirty. You will have to disassemble the amp enough to get access to the volume potentiometer which is soldered to the circuit board. There will be a square hole in it that you can spray some contact cleaner into the control. Use only contact cleaner as anything else could damage the control. Use a small squirt and rotate the shaft. If this doesn't solve the problem you may have to replace the control. While you have it apart, examine the solder side to make sure all the solder joints are perfect especially those on the controls. A bad solder joint can also cause the same problem. Before you take the amp apart unplug the power with the amp on and the volumes turned down. This will discharge the capacitors so it will be safe to work on. I hope this helps.

Your amp has two channels - "normal" and "drive." When you are on the normal channel, the "volume" knob controls your gain. In the "drive" channel, the drive knob controls your gain. In both channels, the "master" knob limits how loud the amp will get.

Most likely, you are on the drive channel, so the volume knob will have no effect. Try pushing the "channel select" switch. You should notice the channel indicator lamp (next to the drive knob) turn off. When it is off, you are in the normal mode. Yellow = drive, and red = "more drive."

Experiment with different settings to get a variety of tones.

To get the most out of this amp, try reading the manual, available online here:
http://www.fender.com/support/manuals/pdfs/manuals_elec/guitarpdf/Hot_Rod_Deluxe.pdf

Have fun - it's a great amp.

There are 2 channels, Which means there are 2 sets of knobs ... One for clean and one for crunch. Start out with a low master volume and set up the crunch, Then the clen and switch between the 2 and make adjustments until they match volume wise ... Then turn the master up.

Here is a link to what your looking for,
http://pro-audio.musiciansfriend.com/product/Yamaha-CM500-Headset-with-BuiltIn-Microphone?sku=245012

I can't tell from the add but hopefully it comes with adapters for both plugs that will work on your mixer. It does have the one for the headphones but the one for the mic is not clear, they are not interchangeable.

You would obviously plug the headphones into the headphone jack. The knob labeled "Phones/Control Room" will control the volume without changing what's being broadcast. What you hear in you phones is exactly what you are broadcasting.

The microphone needs to go into either mono channel 1 or 2. The adapter for it needs to be a mono Tip/Sleeve adapter as the more common stereo Tip/Ring/Sleeve adapter may cause some problems. You can tell the difference by looking at how many sections are on the plug divided by a little black line. Two sections is mono, three is stereo.

Adjust you microphone level by setting the volume knob, the one on the very bottom, to the 12 o'clock position. Then turn the gain knob, the smaller plastic one on the very top, until the desired volume is reached. If you experience any clipping or distortion turn the gain knob down until it goes away. These are general settings, you may want to experiment until you get the best level without noise.