Game stutters 4 times every 30 seconds

I've just started a new project in TGB 1.5 to try out the new ticked physics. I've made a simple helicopter game where the player uses the analog joystick to fly a helicopter in 2D. There's just 1 background image and 1 helicopter image and nothing else, however the game stutters (pauses for about 200ms) 4 times in a row, every 30 seconds or so. It happens if I run the .exe for the game, or run from the editor.

It's as though there's some garbage collection or something going on in the background every 30 seconds that is killing the game.

Here's my onUpdate function for the player's helicopter:

function playerHeli::onUpdate(%this)   
{
	%this.currentRotation = %this.getRotation();
	%this.finalThrust = %this.currentThrust-(mAbs(mSin(mDegToRad(%this.currentRotation)))*%this.rotorTiltEffect);  // add a little extra thrust when tilted, to keep altitude when accelerating
	%this.setImpulseForcePolar(%this.currentRotation+180, %this.finalThrust, true);
	%this.setLinearVelocityX(%this.getLinearVelocityX() * %this.windResistance); // slow down due to wind resistance
		%this.cameraTarget.setPositionX(%this.getPositionX()+%this.cameraOffset); // scenewindow2D is mounted to this to follow the player
}

am I doing anything stupid in this code? Am I using setimpulseforcepolar correctly or is there some way to use constant force to get the same degree of control?

Any help would be appreciated.