mac pro mid 2012 startup chime missing

Hi All,

I have just realised that my start-up chime is missing.

I have done some research & tried to get it back using Terminal & typing in the following :

sudo nvram StartupMute=%00.

However, this made no difference.

I also tried resetting the PRAM - but again, no sound.

Mac Pro Mid 2012

MacOS Mojave 10.14.6

Processor: 2 x 3.46 GHz 6-core Inter Xeon

Memory: 128GB 1333 Mhz DDR3

Startup disk : SSD

Graphics: Radeon RX 580 8 GB

Any ideas?

Many thanks in advance