Clean AC power

The power to my house comes from the pole on the road, then underground to a large box that I assume is a transformer. This supplies power to my house only: there are no other houses within 1000’. Does this mean that I am getting very clean power?
@ vgizzi

The majority of "dirty power" in the home is created by electrical usage items found in the home.

LED lighting.
Electronic ballasts/florescent lighting.
Light dimmers.
Switched mode power supplies.
Appliance/equipment micro processors.
Air handler VFD (Variable Frequency Drive).
Switching on and switching off of electrical motors.
Hair dryers.
Excessive unbalanced 120V loads on the electrical service.
Loose and or corroded electrical connections. ( can/will cause excessive harmonic distortion on the mains.   
Last but not least, audio equipment.

Recently bought a Puritan Audio 156. Major improvement. As oregonpapa said, easily heard, but easily measured with my EMI meter.
I'm using a Audioquest Niagara 1200 power conditioner.  A basic unit with no regeneration. My gear is humbly comprised of a Marantz PM-15S2b integrated and matching SA15-S2b SACD player along with an older model Marantz tuner, my OPPO 103 blu ray player, cable box. TV and a soundbar. 

The sound just got calmer, has a quieter background, there's more see-through, better air and extension in the highs on down to the lows, lost that nervous edge on some music along with some shrillness, etc.

@vgizzi ,
I didn't take any noise measurements; only AC volts which ranged from lows of 118 to highs of 120.4 at any given time of day. At least I knew it was stable despite being an old building. I never took any reading after getting the power conditioner.

All the best,

Look at my system page.

When I installed the Puritan, my readings were cut in half.

Been experimenting with different configuration of all my components. Makes a difference.

Example: My mobile phone charger on a dedicated line ........ the decrease was 10 mV. Have all my wall wart power supplies into my Hydra 8 digital outlet, for an additional decrease of 10mV.