Well you definitely have at least one hive out there somewhere. If this is something different, it may be that a swarm has just moved in. Thats when a hive splits- the Queen along with some or most of the bees leave the original hive and seek out a new home leaving the new queen to continue at the original spot. Fall does not sound like a good time to be swarming cos they need time to get set up for winter....or you have a new hives that have been moved into your area by a beekeeper.
Bees do sound rather loud when they are in a feeding frenzy, which is what it sounds like and sugar syrup will do that.
i would stop refilling the feeders. When they start emptying out, the bees will know that the food source is drying up and they should calm down and move on to your flowers. not too sure what you can do for the birds after that cos as soon as you fill up the feeders again, the bees will hit it hard.
The reason for this is that they are attracted to volume- sugar syrup has a higher volume of forage than flowers can produce- this is also why they say to plant alot of a type of flower if you want bees to work them, one of each just wont interest them. I call it the critical mass.
If you want to try to figure out where the bees are coming from, you can try watching for the direction they fly off too as they will want to get home once they have filled up. One direction will tell you that there is an apiary that way. If they are going off in more than one direction, you have multiple hives around you.
