[Jimbuna]

You could test your theory another way:

Enable the noise meter and approach a convoy at slow speed, as soon as the meter startschanging colour toward orange then red in colour, switch to silent running, your meter should go back to green coloured.

Whilst the noise meter is not an accurate science to informing you if the escorts have detected you or not, it is accurate in letting you know if you are emitting more noise when not in silent running mode.