sharp and piercing high pitch /frequency coming out from Harbeth C7

I agree that you should try a different amplifier with the speakers, and also perhaps a different CD player, though I think the odds are better with the amp.

I had a CJ preamp some years ago that ended up with a bad capacitor in the power supply that generated noise beyond my range of hearing. It was only when my son visited from college and pointed out the issue that I became aware and was able to fix it. 

There is also the possibility that your amp is running out of power when you hear the distortion, but you really didn't say how loud you listen, or in how big of a room.

Lots of possibilities, but you just have to work through all of the components one at a time to find the cause.

One other thought -- there are bad recordings. Sometimes the original master is done using microphones that have their own frequency response anomalies, or the engineer messes with the frequency response -- perhaps because the studio monitors had a dip where your speakers do not -- or due to a number of other reasons.

The problem is that once the recording is released, you as listener cannot do anything to change what is on the CD. The problem with buying a pair of speakers that fix a specific bad recording is that they will then apply the same "fix" to all of your good recordings. And, that "fix" may not work for other bad recordings that have different problems.

I know it can be very frustrating to have a favorite performance that has been poorly recorded, but life isn’t fair. The one possible solution is to buy a frequency equalizer for those situations and see if that helps improve things.