loud engine only at 45-48 mph

so heres my story. bought my aveo a month ago. 06 Aveo LS

so, since i bought it i noticed that the engine would get pretty loud at around 45-48mph. coincidentally i can feel a gear switch happening around that range. still does the same noise even if i put it on hold. thought it was the oil, since it was dirty, so i changed it and put some engine repair additive.

still the same noise. it bothers me.

I dont know if the timing belt could be it, since i've heard that aveos' timing belts go around 60k-70k, and mine is at 73k currently, and i dont know if it has had the timing belt changed.

but aside from this the car runs excellent before and after 45-48mph.

Are you sure its the engine? iirc that is about the range the torque convertor locks/unlocks? and i have heard that that can be slightly louder than "normal"... but how much louder are we talking?

When did you buy your car? mileage?

well the noise is above normal, but not extremely loud, just loud enough that one can tell it isn't normal. kind of like buzzing. just sounds like the engine is trying too hard.
RPMs go down around that range like normal and stay at 2k, but the engine stays loud. it's got 73k miles on it.

you might have an issue with the variable runners on the intake, or again the mentioned auto transmission issue.

1st with the current mileage i would get the belt changed asap, like now! unless you want a big repair bill. i would have the trans checked out and maybe the intake manifold?

thanks for the replies guys.

i'm gonna to a tranny fluid change tomorrow and hope that fixes it since i do feel a gear change at the stated speeds.
so i'll be back then and see if it fixed it. if not i'll ask about the suggestions ya'll gave me.