I'm just guessing on this one. Assuming all of your equipment is OK, since you said this was there from the beginning of this system. First off, I would substitute another pair of speakers, if possible. The crackling statement is a concern, thinking that it could be something else, like too much volume, or another problem. I'm going mainly on the harsh part of your description.
This would help verify if anything is wrong. Also, Paradigm speakers like these have a metal dome tweeter, that some people just can't handle. They usually have a resonance that is right above 20 kHz. That resonance will cause some people that are sensitive to it to not listen at all. I'm one of these people. Also, I've seen several people state they have a problem with fatigue, using speakers like these.
Another problem may be that your amp can be accentuating the problem some. The only thing I have to go on stating this is this review
from Italy. They say the amp is a little bright also. That could definitively be making this problem worse, if this is what is happening with the speakers, assuming all the equipment is functioning OK, and again, not being played too loud.
If at all possible, see if you can try another pair of speakers, that have a soft dome tweeter. Maybe something used, or from a store that has a try, and return policy.
Don't try anything that has a metal tweeter in it, at all. Some soft fabric dome (even soft silk dome) , or a soft poly/polymer type of dome tweeter. These don't normally have this ringing resonance that is common with metal dome tweeters. They talk some about the tweeter resonance here
on another similar model. Also this model
is another example of that tweeter resonance (I call it noise) frequencies not heard by a lot of people. You could see the peaks at the right side (high frequency tweeter side) of the graph called "Frequency in Hz."
If you could do this no cost speaker swap trial with soft dome tweeters, that may be the answer your seeking. This would be what I would try first, if it was me. This is the best I can picture might be happening with your description, except the crackling part. But that may be how you hear it, if your sensitive to it. I hope this helps.