I actually just began getting a similar sound. Was driving around last night, spent 45 minutes on the highway, as I pull off, I notice a "rumbling/gurgling" sound at about 1.5-2.5K. On the highway, doing 4K, the car sounds about the same as it's used to. It's only really the low RPMs, especially in first gear. Revving in neutral when warm it sounds fine. Only when I apply some load it sounds "rumbly."
The car seems to be running about the same.
Staring up the car in the morning, I can really hear that noise. I'll try to record it.
I hope it's just an exhaust leak (the car has 169K) or a cracked exhaust manifold. What are the things I can check for to make sure the engine is OK? Should I put go to an exhaust shop, put it up on a lift and listen for leaks?
No CELs are on and I've driven it for about 2.5 hrs of all highway since then.