Motor current distorted at high speed

[AnthonyK]

Hello,

I am using the FOC with hall sensor (having at 15 degree mechanical accuracy) on a BLDC motor controlled by STEVAL-PTOOL4A. I am using the MCSDK v6.3.2. 

I activated the Overmodulation in order to drive my motor at 18500RPM. However at this speed and without load I have a weird current signal. It is like a noise. However, when I run the motor at 8000RPM the signal is much better and it starts to be sinusoidal when I apply a load on my motor. 

Here are the current:
At  high speed no load

At low speed no load:

At low speed with load:

 

Without OverModulation, at 17000 RPM with load:

 

Can anyone help me with this.

Thank you.