MYRON: it would be oh so helpful if you would give us chassis info to work with. Now we can only assume you have a gas chassis, and going downhill you probably don't have your foot on the gas pedal. IF this assumption is true, then your engine isn't making a lot of vaccum to assist the brakes, and therefore the electric motor powered pump is running to help power your brakes. It probably means nothing is wrong and the electric back up system is doing it's job. However, you may want to check for a leak in your vaccum system.
2016 EC Aspire 42RBQ / 2014 CR-V