I just purchased a 96 Sentra with and automatic transmission. It has a noise that I heard while driving it but I really didn’t think it was the transmission/differental so I bought the car. This is a clattering/knocking noise that you hear while accelerating or cruising on light throttle. It goes away on deceleration. It sound the way a bad CV joint sounds when you are testing one while turning but this noise happens all the time. I don’t hear it unless the windows are rolled but it very noticable then. I have heard noisy water pumps sound this way but ruled that out and I have heard bad differentials that don’t sound this way. You don’t hear it unless the car is moving. The engine itself sounds ok.
It sounds like you’re describing a pre-ignition rattle, which is usually worse under a load (accelerating, passing, etc.); especially if the problem seems to be worse when the engine is warmed up.
There can be several causes for this.
One is an EGR system fault. It will require a little diagnosis to verify exactly what part of the EGR system is at fault but it’s generally not too major.
Two is that since the car is distributor equipped the ignition timing may be advanced too much. Someone could have inadvertently set the base timing wrong (easy to do) while performing a “tune-up” (kind of a bad choice of words).
Another possibility (related to Two) is that someone could have been into the timing chain at one time or the other and the distributor/timing was not checked or set correctly when this was done.
Hope that helps.
I thought about that and dismissed it, although at this point I won’t rule it out completely. I have a pretty extensive background with cars and this just sounds way to mechanical to be detonation. And today while driving I noticed that I can feel it just slightly in the steering wheel.