Before my car destroyed it's bottom end, it used to fire up, and almost the moment it did, the Defi oil pressure gauge warning stopped sounding.

Since it's been rebuilt, when I start it, the sounder goes on for about 2-3 seconds before it stops.
Is this normal? It runs 7-8 bar cold and minimum 3 bar at tickover, hot.

 

mine stops buzzing as soon as it fires

 

Dunno about the buzzer but the readings are good !

my classic, original engine/build is 6 Bar cold 2 bar hot

 

Your running-in oil a bit thin ?

dunx

 

Might be a bit of air in the transmitter block causing a sluggish response, won't do any harm and prob go away in time.