Too be honest I can`t remember if it was quieter or not,maybe- but it did sound different to the MR2,probably due to the new larger intakes and the various odd shaped sensors.
I have always been a big fan of the Nimrod-the tragic loss of the MR2 over Afghanistan,was down to poor design and penny pinching,with the air-to air refueling system.
This had been completely redesigned in the MR4 I believe,yet it was never given a chance;to be honest I blame the US for pressurising the UK Government into using their aircraft,in much the way they bullied the Labour Government into scrapping the TSR.2 project and tried to get the UK to buy the F-111.
Well that`s my theory.