Volume differences in aliased sounds

Many of my FS9 (pax) jets have their sounds aliased to one of them which has my preferred sounds. You would then expect that their sound volumes would always be (more or less) the same in each of them. However, the differences range from "normal" to extremely soft, giving rise to the idea that these differences are somehow aircraft specific, but there seems to be nothing in any aircraft,cfg or .air file which could be related to aircraft specific sound volumes.

It makes no difference when such aircraft sounds are "un-aliased" and all of them use direct copies of the preferred sound folder. Default ATC sound volumes can also differ widely.

Ideas anyone ?

Thanks in advance.

Hans