Solved! Amp or speakers sounding muffled

[enufbp]

Hi everyone,
I've got a Onkyo A-9010 and some Q Accoustics 3000 Series speakers set up in my living room, as well as a Rega Planar 1 turntable (am relatively new to all this, and this seemed to be a good entry level set up). Recently, the sound has started to sound muffled. I've ruled out it's not the turntable (after cleaning the stylus, and connecting the amp to my phone via a jack). I've also rewired the whole set up, and it still sounds the same.
Does anyone know what else could be causing it, and what tips you could give me?
Thanks

 

[americanaudiophile]

Is the treble control of the Onkyo at 12 o'clock? That's the flat setting. Can you hear the difference when you turn that control?
If not then the tweeters on your speakers may not be working. You should be able to hear the difference when you block the tweeter with your hand.

 

[enufbp]

Is the treble control of the Onkyo at 12 o'clock? That's the flat setting. Can you hear the difference when you turn that control?
If not then the tweeters on your speakers may not be working. You should be able to hear the difference when you block the tweeter with your hand.

Thanks for the reply. Yes, when I turn the treble fully to the right, it sounds better. But it's always sounded fine at 12 o'clock until just recently - we've not moved it before.