I have a 2002 honda accord ex 2.3L 4 cyl VTEC coupe. When accelerating, I can feel a vibration in the gas pedal and the engine sounds louder than I am used to. The vibration is not large, it feels like a resonant frequency within the engine. The engine noise is not real loud either, just louder than it normally sounds. It sounds like it is running at a higher RPM but the RPMs are where they should be for the entire range of speeds. When idling, everything is completely fine, there is no extra noise or vibration, only when accelerating or driving at higher speeds. The only other thing wrong is the transmission is shifting a little late coming out of second. Sometimes when it goes to shift, the engine will rev up for a sec first and then the transmission will catch. This only happens in 2nd gear and occasionally 1st. The engine was just taken out for what was supposed to be a rebuild. The piston rings were good but the valves were all replaced. Also, a pressure switch on the transmission was replaced. All gaskets are new and as far as I can tell there isn't any kind of exhaust leak making the noise. Any clue as to why there is a vibration that was never there before? Also, is the shifting problem something that could be caused by replacing the pressure switch and not doing some kind of calibration with the computer? Apart from the vibration/noise and the occasional shifting issue, the car is driving perfectly. It has good power/pickup, and usually shifts smoothly all the way up and down.

 

If the engine was removed for the recent work, I'd check for the exhaust system alignment. It's tricky to get it all back together just right. When you accelerate the exhaust system can move so maybe it just begins touching the floorpan of the car & that's what you hear.