What triggers the seat belt & no smoking sign dings?
For some reason on the ground I don't get the ding (only in-flight)

Same question for autopilot ALT alert - it doesn't sound

Same here

Yeah me too no seatbelt or flap movement sound in the cockpit

Shom wrote on Jun 2^nd, 2018 at 5:44pm:

What triggers the seat belt & no smoking sign dings? For some reason on the ground I don't get the ding (only in-flight) Same question for autopilot ALT alert - it doesn't sound

These sounds are programmed according to the 757 FCOM. There's a number of conditions and they work exactly as they supposed to.

Ang wrote on Jun 3^rd, 2018 at 8:52pm:

no flap movement sound in the cockpit

The flaps is a bit different story but they are there as well.
If you think they aren't loud enough you'd adjust the volume in the sound.cfg

What about the autopilot altitude alert? It doesn’t sound

Shom wrote on Jun 4^th, 2018 at 9:27pm:

What about the autopilot altitude alert? It doesn’t sound

When it supposed to sound according to the manual please?

Also not having any of the cockpit sounds, i also adjusted all volumes to max and still nothing.  Took it off auto pilot and nothing. From my previous flight of 10 minutes ago. 

But the engine sounds... are great now! :D