knocking sound around 70 mph??

I just recently bought a 2006 suburu forester. It is my first Subaru. I noticed shortly thereafter when I get up around 65-70 it starts to make a noise. It sounds like a knocking noise or almost like a tire noise. But only does it when it is accelerating at higher speeds. Should I worry about this or is it how the h4 engine sounds?

Well, as a whole, Subaru engines tend to be a bit noisy. On the highway you shouldn't really be able to hear it. Are you sure it isn't tire noise or something loose? Some Subarus have a removable cover for oil filter access, sometimes if it is loose it can cause a fluttery/knocky kinda noise.

I don't think its a tire noise because as soon as you let off the acceleration the noise stops. It actually begins around 40 mph, but you can really hear it at 70. It only does it when you are accelerating at those speeds. As soon as you let off the gas it stops.

I don't think its a tire noise because as soon as you let off the acceleration the noise stops. It actually begins around 40 mph, but you can really hear it at 70. It only does it when you are accelerating at those speeds. As soon as you let off the gas it stops.

You might need to have the valves adjusted, I really can't think of any reason the engine would make that kind of a racket at speed.

I don't know its the engine. I think it might be in the drivetrain like a pinion bearing or something of that nature. Or maybe a uv joint.

Is it auto or manual?

auto