When starting from cold, stationary tapping from underneath vehicle. When in drive still tapping louder until at steady speed on smooth road tapping seems to disappear, suspect exhaust knocking but not much movement when tested when cold. Any ideas please

 

Is it rhythmic? Only when moving?

I had a weird thumping occasionally under my 97 when I first got it. Turned out that the plug for the rear O2 sensor could just touch the front u-joint every now and then and it would get dribbled like a basketball against the transmission tunnel. Sounded like someone was under the car with a jackhammer.