sync~ Macbook and power supply

Jabbo's icon

Anyone experienced this?
Sync~ object in Max 5 becomes unsteady when my PSU is disconnected.
I tried it out, and some times when I disconnect my PSU from the Macbook after a little its starts to be unsteady.
Tried out with the help patcher too.

Macbook Intel 2GHz
10.4.11
Max 5

by unsteady I mean that the output (audio and MIDI) manifests discontinues jumps in values.

thanks