Chelsea 150 BMS buzzing noise?

[twinx]

Hi from Michigan:
I just took delivery of 3 Chelsea 150's and have a strange resonance noise from all three. It happens during part throttle and sounds a lot like a heat shield or something like that. The sounds is worse at heavier throttle loads (still breaking-in so not that heavy) and sounds like something that will need immediate attention, if you know what I mean. Overall, very pleased so far and the paint is beautiful considering the price point of these units. As far as quality is concerned the PDI and necessary repairs are taking a while to get sorted out.

Thanks for any input.

Jim Mc.