Do you hear them at any speed, or while turning left or right, which is more likely.
A good test is to jack the front wheels off the ground slightly, put a BIG bar 90 degrees to the tire under the wheel and lift up. If the top of the tire moves in and out, or you hear it click, you most likely have loose bearings, and they will wear quickly.
Repacking wheel bearings on a car is no big deal, but on a Seneca,
(C-5500) those are BIG tires, and I would leave it to a shop with the proper equipment.
They should be good for 100k, barring a bad bearing, so don't kick that dog if you don't have too.
Mike in Colorado