I see few issues with Civic autos that have had at least a few fluid changes.
The drone you're hearing, check the entire exhaust from front to back. If this car is equipped with a "catifold" (manifold and cat integrated into 1 unit) they have a very large propensity to crack. They leak when cold and cause really odd vibrations at certain rpm ranges when running.
Does the drone go with engine rpm, road speed, etc. Does it stop if you shift it to neutral at speed and let the engine idle?
Thanks for the very informative response, Fred.
I am not really knowledgeable about the car's exhaust so I might have to read up a bit more to determine if it has catifold or not.
As far as the droning noise, we will probably wait till after we replace the old tires on the car with new ones. Again, I doubt it has much to do with tire/road noise, but strangely that noise doesn't seem to affect the way the car drives either so far. If it's still there and as loud as before after the tire replacement, then obviously something else is wrong(like the exhaust as you mentioned) with the car.
Yes, the drone does seem to go with engine rpm. I think it begins at around 1,000 rpm and peaks(loudest) between 2,000 to 3,000 rpm. I haven't really driven the car on the highway so I can't really be sure if it's any better or worse at higher rpms. There is no drone at idle when car is not moving, but I'm not so sure whether it does this when shifting to N as it moves though.
I think you're right on target, Fred. I just read up a bit more and it seems cracked exhaust manifolds is also one of the more common(maybe not as common as the 4AT failure) problems on 2001 Civics. I also looked closely at the service/maintenance records and noticed that the catalytic converter has already been changed. I don't know if it means anything but hopefully it's nothing too serious. We'll definitely get the exhaust checked and will report back the findings.
The tranny fluid has been changed twice, once at 60k, another at 120k, so it's definitely due for another change very soon(I'm not gonna wait till 180k lol).