A question about how my strings sound.

[Nighthawk99]

Hi guys,in the last month or so,my 1st and 2nd strings(E and C)have started to sound odd when I'm up around the 12th fret marker and slightly higher.
The only way I can think of to describe it is they sound like a badly tuned pub piano or a honky tonk kind of sound if that makes sense?They're not ringing clear as they should.
My digital chromatic tuner is spot on..not sharp or flat..when I check the tuning,but I only do that on open strings.Any ideas please re what's causing this?
Thanks in advance
Roy

[Danny Mitchell]

Hi Roy,
I wonder if you're not damping the strings adequately behind the bar. Up at the 12th fret this would cause a chorusey, detuned effect.

[Nighthawk99]

Hi Danny
Looks like that's what was missing,I wasn't damping them enough behind the bar.
I've tried it and now it all sounds better on those strings.Cheers for that!
Roy