Transmission?

I got a 2003 used a year back. It recently had front wheel repairs (rods, bearings etc) but otherwise hasn't shown any problems. Within the past 2 weeks, the car has started making a much louder humming noise when switching between gears (a little revving hum is natural of course). Now it sounds like it's straining itself. There is no jerk or pause and it still runs perfectly smooth with no reluctance. The humming is the only thing and it only hums when moving up gears. Today, the check engine light came on. This has me fearing for my transmission. I really hope there's another cheaper issue. haha My fluids are fine as well. I'm hoping to take it to Autozone or somewhere soon to identify the error code. What do you think? I made this account to ask this question but I can't imagine it will be my only question about Regals so I look forward to your help.

Thanks!