1998 Chevy Lumina Lumina sounds like it's straining

My 1998 Lumina has always run extremely quiet (you could hardly tell it's running when stopped), but a few months ago it started idling louder, sounding like it was running higher RPMs whether idle or accelerating or running a constant speed. I can also feel extra tension and vibration in the gas pedal.

For the first few weeks the problem was intermittent but now it is constant and seems to be getting worse. It still drives fine and seems to have enough power, I'm just worried that this could indicate an impending bigger problem. Any ideas? Thank you.