Q:

What goes around comes around

Speak and I shout 
You say it once and I come aloud
For I say alike 
Invisible to your eyes,
Ears are my friend,
Because they understand.
To be my friend you have to take a hike,
Where its all crisp and white.
Tell me what am I?

A:

It's probably

 echo

Speak and I shout

 echo is a sound

You say it once and I come aloud 
For I say alike

 it just "repeats" what you say

Invisible to your eyes,

 sound is invisible

Ears are my friend,
Because they understand.

 but you hear the echo

To be my friend you have to take a hike,
Where its all crisp and white.

 the mountain is often a great place to hear your echoecho

A:

A slightly different take on Kant1's answer, I'd guess you are: 

 AN AVALANCHE 

Speak and I shout
You say it once and I come aloud  

 A relatively small sound (like people speaking loudly) can trigger an avalanche in popular culture (e.g. Tintin in Tibet)
 Yet, with that sound, the avalanche makes a much louder thundering sound  

For I say alike
Invisible to your eyes,
Ears are my friend,
Because they understand.  

 The start of an avalanche is often heard/felt than seen, especially if the mountainside is cloudy  

To be my friend you have to take a hike,
Where its all crisp and white.  

 You need a snowy mountain as one of the pre-requisites for an avalanche 

