What kind of pump? Does it have alot of hours on it?
Are you sure the isn't any air in the pump? (probably not, that doesn't go away when you pick it up)
Can you feel the noise when you pick it up?
The impeller maybe cracked or just have gunk on it throwing it out of balance. Take it apart and look for slime, small gravel or chipped/cracked/even out of balance impeller (could come from the factory like that too).
Let ups know what you find.
Dr Joe
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