First off weather can play a huge part in when the bears move, I have always found storms, rain or heavy winds are not good conditions for sitting on a bait waiting for bears. So yes this can play a part, especially seeing the bears appear to be in close proximity to your bait.

I would start or try refreshing your bait as early in the day as possible and pay no attention to your scent, in fact you want it as many bear's will circle or come in down wind to the bait. Basically by paying little attention to what scent you leave you are conditioning the bears to your presence. The grease thing is good but once I have poured out my circles a few times I pretty much stick to hanging jugs in trees with a small hole pierced in the corner to provide a drip or pour it on rotten logs/stumps. When I use plain bread's I will also often mix the fryer grease, molesass and icing sugar..if sweet breads then no need for this mixture. The most important thing you need to do is contain your bait some way, even a small bear has little troubles rolling and moving logs. Once one bear has done this it becomes easy for every other bear and critters to horn in on your offering. Thus the barrel chained to a tree is the preferred method, it allows them to eat but it also limits them. Pretty much a fine line you have to walk when baiting bear it falls between not enough and giving them to much. I believe in feeding them but also in teasing them so figure out ways to drive the bear's to want to be at your bait longer and more often.

A radio may work for a day or two but once they become accustom it will do nothing but waste batteries. Sitting on your bait all night to prevent is counter productive, please refer to above statement of you want them to be comfortable with your presence! This is not deer or elk hunting, when dealing with bears and bait they will and do cirlce you. Yes they know your their but really boils down to if he is conditioned to the offering and the scent that accompanies that offering he will come in on his own terms...most often than not he'll look you square in the eyes, ponder and then proceed if he see's no reason to flee. I don't think I have ever been in a treestand looking over a bait when a bear didn't look up either while on the bait, coming in or circling..the nose is great, the ears are good but eyesight is aweful on bear!

Best of luck and hope it helps you in some way!