I spend about 2 hours a day driving in my car, along with a few hours sat at a desk working. I was wondering if anyone can recommend some good audio to listen to (e.g. Podcasts, ear training exercises) that can help learn music theory, without requiring me to look at a screen or have an instrument in front of me? (I know this will limit the options somewhat)
With most things it is good to try and multitask. When learning new things it is not good to multitask. If you are doing two things, only 50% of your brain will be dedicated to learning, and you'll learn half as much material half as well, and you'll be half-satisfied because of it.
My philosophy is that if something is really important enough to you, you'll make the time for it in your day.
Aural skills and music theory are two entirely separate enterprises. For the former I recommend you get a solfege book and learn to sing. For the latter I recommend getting a theory text and workbook and going through it cover to cover.
I second jjmusicnotes, in that music theory is not particularly amenable to passive learning. Particularly if you have any intention of using the theory to understand or compose music. It's going to rewire your brain if you do it right.
I recommend taking the plunge and signing up for a Freshman-level Music Theory course at your local State U or Community College. These almost always have an accompanying Aural Training/Listening Lab component. And being Freshman-level, have few or zero prerequisite requirements (just the desire to learn).
If you're like me (and many other musicians) self-discipline is a major issue in such a big undertaking. Being forced to show up every day will really help you keep up with it.