I agree with @lewm , give them a try. It could be part of the structure you hear, but it would not be a very loud sound.
If there is a rattling sound, it could be a small piece of the plastic base is loose inside. I’ve had a couple of these.
In any event, contact the seller and ask what he thinks it is.
If there is a rattling sound, it could be a small piece of the plastic base is loose inside. I’ve had a couple of these.
In any event, contact the seller and ask what he thinks it is.