probably a pinhole in the insulation going to the cathode causing the 10,000 volt power supply to arc. get a new TV. that one is now a fire hazard.

 

hope not, this one is brand new like 2 years ago. h:

 

if it's a loud pop i'd almost gurantee that's the problem.

 

It's normal, and you're probably just a light sleeper. It's usually to do with the expanding and contracting during the cooling down process of the metal funnel part of the TV. It expands when it's on and during cooldown, there are instances where it just moves quickly to adjust itself... much like an earthquake between two slabs of crust.