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

if you switched amps and speakers and the sound is still there - then it may be your source, or even cables, if its some kind of emi (airborne noise pollution captured by rca cabling)

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.

This is definitely not a speaker malfunction.  Your problem is up your equipment chain.

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.

Which is why you need an equalizer in your system. It should be illegal to sell speakers without EQ. 

Both channels?  Equally?  Tried swopping L and R connections?