Same here, pls provide the information directly from Coinbase, can't find it myself also. Even though Coinbase is a respected and trustable exchange, they will never give 5% per day, that's too good to be true. If this would be real, they would go bankrupt soon.
If the information on the Reddit link that vv181 provided is correct, your funds from the Coinbase wallet are redirected to an external miner website... Personally, I would stop using it as chances exist that you will loose all your money.