I can now confirm that this is definately a problem with the laptop (i know i know - you've been saying this all along).
How have I confirmed this? You know the regular 'tick' that happens every 8-9 seconds is so regular that if I jog for about 4 secs then don't jog for 2 seconds and then jog again I get the tick at the 3rd sec i.e. similar timing to jogging continuously.
This tick does not vanish even with different microstep values.