High frequency distortion?

Hello all, I'm newish to vinyl, having gotten my first turntable, a Denon DP 300F within the past 12 months. It's been great so far, but lately I've been noticing distortion in both channels, mostly with high frequency sounds, like cymbals, high guitar notes, high vocal ranges, etc. Pretty much anything that comes out of the tweeters. All of my records were purchased new, so they've only been played within 5 times each. Anyone have any idea what could be the cause of the distortion?

Troubleshooting I've done:

• Hooked up different speakers to the receiver.
• Unplugged turntable from phono, and into cd, then used the turntable's built-in pre-amp.

• Plugged headphones into the receiver while playing a record.

  In each case, the distortion persists, in both channels, at the high frequencies. Thank you so much to anyone who can offer any insight.