Hi there,

It sounds like it may be an issue with the guitar. If you haven't done so already, I recommend re-stringing your guitar. Even if you bought a new or used guitar from a store, it's no guessing how long those strings have been on the instrument. Re-string the guitar might help with the dull sound.

The twangy-ness and the strange reverb might be from rattling of the strings. It's possible the string action is a bit too low. You may want to adjust the string height.

What kind of guitar do you have? Acoustic or electric?

You might want to check out how to adjust string height in this lesson by Gary: https://www.guitartricks.com/lesson.php?input=28444

Jump to the 6th minute mark for string adjustment tips.