[Bimmer]

Partially solved the problem, at least for the P-51s. I found that there was a capitalization mismatch in the names of some of the sound samples in the motor.Packard-Merlin.prs file, specifically in the capitalization of the "M" in Merlin. Correcting this got proper engine sounds back for all the P-51s, both internal and external. Apparently the text of the .prs files is case-sensitive.

Now I need to figure out which files are used by the other aircraft types having this issue.