If anything it could be a case of too much power (and incorrect technique). *If youre still learning to texture milk you may want to consider replacing your 5-hole tip with a 2-hole. *
Sounds like you are putting too much air into your milk. *If youre going from 400ml to 600ml+ then you must have large bubbles in there. *You should be aiming for a smaller ratio of foam and a nice velvetty texture.
Try watching Scottie Calahans video to start with:
If you recently bought the machine new you may want to contact your vendor and ask for advice or even better, a demonstration. *Each machine is slightly different.