Canon 70-300 mm IS USM motor-like sound which lasted for a couple of seconds while half-pressing the shutter button to focus, is this normal?

1. First of all, make sure the lens is aligned properly and it's not loose in any way. The camera will immediately recognize the problem and will not let you fire the shutter.

2. Allow your lens to auto focus on an object (preferably something that's on your wall). See if it detects the object when you half press the shutter, and once it does press it down all the way.

3. If this is still not the case, the lens itself may be causing the problem. Make sure your camera is compatible with the lens (though most Canon lens are compatible with the EF-S series, it's still wise to check in Canon.com)

try cleaning the contacts on the lens and on the camera. Remove lens first.
Use electrical contact cleaner. if you don't have any, try rubbing alcohol.

Sounds like a loose screw inside shorting out one of the curciut boards! tccamerarepair.com

Your flex cable to the Iris is broken. Have a look at my gallery at http://www.pbase.com/barry_2718/efs1785mm I have the same symptoms. At 28 or 35mm it make work ok. try Av mode and f8 aperture to see if you get an err01 because the aperture does not move either.

Which camera body do you own? It is the camera that determines where to focus and when you are in focus or not. I have 3 Canon film bodies and two digital. On all, the camera can be set to detect focus using all or a specific focus point visible in your viewfinder. Check how you have the camera set and choose ONE focus point. place this focus point on your most critical item in the image, in the case of your birds, the HEAD of the bird, press your shutter button half way to lock exposure and focus, then shift the aim to compose your image before pressing the rest of the way to make the exposure.

For birds, on my digital cameras, I choose to go into live preview mode, zoom in to 10x magnification and manually focus. This eliminates the camera not knowing what I want in focus.

try using a tripod to steady the shot, and do not forget that Canon states you should turn off the IS when the lens is used in conjunction with a tripod. From firsthand experience, I agree with this instruction, often when stable on a tripod, the IS can actually be trying to correct for its own movement and cause a degradation in image focus.

Good luck

There's a button with a clock next to it. Press that button and put your camera where you want it. Press the shutter release half way, to get focused. When you press it the whole way down, the timer will start and you will have 8-10 seconds. There is normally a burst of a few flashes when it takes the picture.

It is normal that when you press the shutter button half the flash won't fire because you're focusing on a subject upon pressing the shutter half way

It's just like you are locking a subject upon pressing the shutter half way

Sounds like your custom functions have been changed to work this way. On the EOS 350 D it is Custom Function #04. To change it back to default you need navigate through Canon's menus. Here's how to get there: while in one of the creative zones go to your camera menu and navigate to the 5th tab on the right. Select “Custom Functions (C. Fn)” from this tab. This will open a submenu of numbered options. Select #04 and set it to 0: the default AF/AE lock on a half depress of the shutter. That should get your camera back to the expected auto focus with the shutter button.
Happy shooting :-)

There are two stages to the shutter release. The first stage is the focus stage pressed half way down and the second stage is the actual shutter release. Always press the shutter half way to get the camera focused first then press all the way down when the camera is ready to take the shot. Check to see how the settings are with regard to how it focuses (9-point, face recognition, etc). When the camera focuses you should get a green box or multiple green boxes depending on your settings. That tells you the camera is ready to take the picture. Pressing the shutter all the way down at once from the beginning will cause the pause you describe since the camera has to first focus then shoot the picture. Depending on the subject or subjects the camera may take a second or two longer to focus. With good lighting my G9 focuses pretty fast. Hope this helped.

The USM focus works by applying pressure to a set of rollers. That pressure is achieved with a large diameter spring washer. It is held in place by another large diameter flat washer that on assembly is rotated 60 degrees to lock it in place. If the lock washer has moved due to mechanical movement (ie rapid manual movement of the focus ring) it could unlock and then all pressure to the USM motor parts and rollers is lost giving the loose feel you mentioned.

You will need to dissassemble the rear of the lens to see the USM motor parts, rollers and locking ring to reattach it. Follow the links at my pbase gallery to see the dissasembly. When I took my lens apart the focus and USM motor went all loose and I wondered how could it work ever!!!. The locking ring was off which sounds just like your fault. http://www.pbase.com/barry_2718/efs1785mm I also have a flex cable cracked which is a much harder fix. Take careful note of the parts (mark then with a felt marking carefully) to achieve a reassembly exactly as removed.