Wii controller gives a high frequency noise all the time

It may be the control itself too. In time, these controls can get dust build up inside it. There are volume control spray cleaners available from Radio Shack or other electronic parts stores. The cheat on cleaning the control is to just rotate it from stop to stop as many times as it takes to clear the noise.

If you have over driven the amp by playing it real loud with the bass control turned up, it is very possible that you have toasted the output stages of amp.
Every time you boost a tone control by 3 db you have doubled the output power at that frequency. So if you are "coasting" along at a nominal 75 watts, the moment you boost the bass by 3 db the amp has to put out 150 watts at that low frequency.. Go to +6db and now the poor amp has to kick out 300 watts! And so on.

Rule of thumb - you never use your tone controls at very loud levels. Tone controls are there to compensate for the poor frequency response of the human ear at low volume levels - the Fletcher Munsen effect. At low volumes our hearing with the lows and high frequencies so when you play something at low volume you boost up the bass and treble to compensate for poor hearing. At loud volumes our ears respond properly.

A capacitor is more like to fail than a coil, so I would also suspect a cap first. Capacitors conduct high frequency more than low frequency, so this may explain the extra load and shutdown on high frequencies.

"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.

Reduce the volume level.

I would suggest your crossover unit has failed in the speaker cabinet. The crossover circuit board separates the low and high frequency content of your stereos audio signal. The low frequencies go to the bass unit (woofer) and the high frequencies go to the tweeter speaker. If the capacitor on the crossover goes open or near open circuit then noise is introduced into the sound system. Replace either the capacitor or crossover unit.

Volume/Squelch control: As desired
ETone: Sets the sound of the echo as desired
MicGain/RF Gain control: Normally, leave fully clockwise
Band Switch: for CB, turn all way to left (a/e)
Mode Switch: Selects how you modulate the radio. Normally, you will operate on AM, USB or LSB.
Fine/Coarse control: Changes the frequency you operate on. Normally, set so the frequency counter reading ends in 5. (center slot of the channel).
Buttons:
RB: Roger beep. Turn on or off as desired.
NB/ANL: Noise limiters. Leave on.
Frequency Counter: Turns counter lights on and off.
+10 KHZ: Allows you to get the channels missed by the Channel knob. Normally, leave off.
Power: Selects either high or low transmitter power setting.
Band: Selects band of operation. Low (A-D) or High (E-F)

What you need is a Plug-in, Either a NOISE FILTER or DNR (Dolby Noise Reduction) Also try when you record to set up the Mic away from Speakers, Equipment, and watch your lights. These are all Noise Makers on Tracks. Even Guitar and Bass to close to Monitors will give you added noise. If you can not find a Plug-in then pull up an EQ, Find the Frequency making the Noise, Adjust the "Q" (Range of Frequency) to be NARROW, Then slowly pull down your unwanted frequencies. This will get rid of Noise, But also anything else in that Frequency! Good Luck!

this can be caused by a few things, depending on the type of phone and where it is....if the phone has a built in amplifier, the whistling could be caused by acoustic feedback due to the volume level being set too high, also your phone could be picking up some stray frequencies from somewhere, eg flourescent lights, or radio frequencies, a hearing aid, or there could even be fault on the phone line.... sorry to seem so vague, but without more specific information were fishing for clues.

THE MUTING CIRCUIT IS ON AND IT CANNOT BE DEACTIVATED BY UNPLUGGING UNIT...YOU MUST HAVE THE REMOTE TO DEACTIVATE.