Loud roar coming from 07 Kia Sportage?

Hi guys, I’m hoping you can help me, as I am a bit puzzled. A bit of back story, I was driving down the highway one morning, when the spare tire from a small truck in front of me falls off on the highway. I’m probably going between 40-50 mph, and I can’t change lanes, so I hold my breath as I drive over it. I thought I had cleared it when I heard the tire hit my 2007 Kia Sportage somewhere around the backseat area. Kia continues to run fine, no fluids leaking, engine running normal, transmission running normal, etc. Our car has never been quiet on the inside, but we noticed that the road noise started to get louder and louder. We knew that it was getting time to replace our tires, so we figured that is why it was getting louder. I had the tires changed, but the noise was still there. And it gets louder. But everything continues to run normally, and my mileage is not affected. But it gets louder. And louder. I thought maybe it cracked the muffler, but you don’t hear noise on the outside, just the inside. I just passed my state emissions check, so that is ok. I haven’t taken it to a mechanic because there hasn’t seemed to be any other problem, other than it’s just loud. The noise seems to build up as I am gaining speed, gets its loudest about 50 mph or so, and at speeds higher than that it goes down slightly. It doesn’t coincide with the transmission shifting, and it shifts at the same RPMs it always has, no issues there. The noise seems to be coming from the back of the car.

I have no mechanic, I don’t want to go find a new one and not have any inkling of an idea of what the problem is. Can anyone help, please?

It sounds like the tire knocked something loose. The possibilities are myriad, and the only way to find it is to get the car on a lift for a good look-see. Got a reputable shop in town?