I am pretty sure "sound of power" can be disabled.
I'ts an nice feature but sometimes needs tweaking or just plain doesn't fit.
A real E7 got louder the faster it ran and the harder it pulled, so the decoder is functioning prototypically.
You can download the QSI Technical Reference Manual from their web site or from BLI, which may have a CV setting that can be changed to adjust the "Sound of Power" feature, which is probably what needs to be adjusted.
Join the Broadway, BLI, forum and ask there if no solution here. I have the PCM F3 by BLI but it has the LokSound.
http://www.broadway-limited2.com/forum/index.php
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.