Possible cause of harsh mids?

Thanks for the replies, gents.  Certainly only on a few albums so far.  Not sibilance per se, but more of a distortion on peaks in the mid band - guitars, keyboards, etc.  Bass and treble not an issue.  For example, another one that does it is an old Stanley Clarke album.  (Funny that it's Corea and Clarke!)  First song starts out with some drumming and bass for maybe 30 seconds and sounds good.  I'm thinking, good score for $4!  Then the guitar starts in and it's instant distortion. Grrrr

Brand new Rega P6 with exact cart.  I think I have it set up pretty well.  Most albums sound very good with no problems.  Other than the normal pops and ticks of course!  A definite upgrade from my old Dual.  I am leaning towards bad pressing or just plain worn out.  I am taking notes and will do a good cleaning asap.  Maybe that will help a bit.

pk, I just had another thought. The Exact cartridge has an extraordinarily high output, 7 mV! It may be overloading your phono stage. Here is the inexpensive way to figure it out and fix the problem. Go to Digi-Key and get a few of these, https://www.digikey.com/en/products/detail/stackpole-electronics-inc/RNF14FTD2R00/1974192
They are very high quality metal film resistors, 2 ohms. They will cut the voltage in 1/2 to 3.5. I would insert them right at the cartridge. Cut the resistor leads short, solder a cartridge clip to one lead solder the other lead to the red tonearm lead then cover the construct with red heat shrink. Do exactly the same to the white wire. The resistors are like 15 cents a piece!  If it does not work just return everything back to stock. If it works and sounds fine you have fixed the problem! If you decide to try this let us know what happens please. Another way to get an idea if this is the problem is take the record somewhere where you can hear it on another system and see if it distorts in exactly the same place. If it does then it is the record, if not then it is your system and the cartridge overloading the phono stage is an excellent candidate for the prize.

I was going to offer the same explanation that @mijostyn did - the extremely high output of the Rega cartridge might be overloading your phono stage.  If you have lower gain settings on your phono pre, you might try that.  Or if you have another cartridge with lower gain, you could install that to do a comparison.  If you don't have another cart, you can pick up something cheap like the Audio Technica AT-VM95C for $39 to give it a try.  And having a cheap, backup cart is never a bad idea in case you accidentally damage the Rega cart.