Noise on the left side of the keyboard?

If the noise is coming from the left side of your keyboard, it's unlikely to be a hard drive noise, since both the optical drive and hard drive are located on the right hand side of the machine.

Having recently upgraded my hard drive, I noted that the logic board and battery take up the left hand side of the internals, so not quite sure what could cause a noise.

If your MacBook Pro is still under warranty, make an appointment at your local Genius Bar and get them to check it out. If your MacBook Pro is out with the warranty, they'll be able to give some indication of repair cost.

The only moving part on the left side of your machine is a fan, so unless the noise is actually coming out of your left speaker and can be stopped by muting the audio (press the F10 key to mute it), the fan is undoubtedly the culprit.

It looks like the sound comes from a external port? Is that possible?

Not unless the sound is coming from somewhere else inside the machine and you hear it when your ear is pressed against the ports. None of the ports ever emit sounds by themselves.

The sound looks like a disk head rolling?

A sound can't be seen, so it can't look like anything.

In rare instances, the CPU and/or GPU can emit noises, and if the noise increases when you begin a download, perhaps that's what is happening in your machine. Take it to an Apple Store or authorized service provider to be evaluated.