Morning all.
It sounds like a minor spit back through the throttle bodies, most petrol engines do this sometimes. It's more common on engines with fewer cylinders like a V twin, as the cylinder that's firing effectively has to do more work, as there is comparatively more resistance from the other cylinder. As compared to a 4 cylinder engine where the firing cylinder is assisted by other cylinders that are on the down stroke, (it's all torque you know)
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As, like you said it's the running in period I wouldn't worry too much about it.
Most engines do not perform their best until they're fully run in.
It would be worth mentioning it at the 600 mile service, just in case there is a slight leak on one of the inlet manifolds, or on one of the vacuum hoses.
Cheers.