1997 V6 Accord Engine Noise

My new/used 1997 V6 accord has a low frequency rumble / noise / vibration at around 4000 rpm or 70-80mph. It's not very loud but I think a V6 should run smoother.

The only thing I have noticed is a dent in the exhaust header where it collects to one pipe under the car. Must be from a curb or rock. Could this dent cause an exhaust restriction and noise or is there another common problem with this vehicle.

Thanks

does it only happen at that specific time that u said or does it happen at other times to? Do u notice the sound increasing in frequency and/or loudness as the RPMs rise or speed rises?

The rumble is fairly constant showing up at about 4000 rpm and gets a little louder as you increase but stabilizes in loudness and frequency even as I speed to 80+