Welcome beelady Thanks for starting a thread. Aggression in bee hives can be hard to figure out at times. Weather, loud noises, vibration. other animals or insects (Skunks, raccoons, mice, hornets Yellow jackets) can all make a gentle hive become aggressive. I have even seen where tree branches knocking the hive in the breeze has set them off. Sorry to say I have seen some people being to close to a hive causing the bees to become more aggressive.
Other things, to much smoke, perfumes, scented soaps, bananas, dark colors, and many more.
Time of day go into the hive between 11am and 3 pm as that is when most of the bees will be out foraging.
and lastly the calmer you stay the calmer the bees will be.