noise removal from signal

[nareshjaiswal]

I am carrying out experimental modal analysis
I am exciting the structure by Impact hammer
and response is being measured with accelerometer.
When there is no excitation, theroretically  there should not be any response from accelerometer.
But without excitation if I capture signal from hammer (force) and accelerometer
I get some signal. I believe, it is a system noise or measurement noise.
I have attached herewith some samples of measurement noise, and actual signals after excitation.
My question is how to remove the 'measurement noise' from the measured signal?

Could you please help?

[Henrik_Volkers]

Most simple way: just align all wavefrms from repeated measurements (force slope) and add them. 

Signal will add, noise will mean out with sqrt(n)