Hi Expat,
I'm sure Todd will chime in as well, but I'm his "partner in crime", producing his videos (though this one pre-dates me), handling the website, etc., so I'll take a stab at solving your issue.
Not sure if you're using the downloadable version or the DVD but, compression aside, they are identical. Are you, by chance, using a laptop computer to view these? The *only* time we've heard of this with these videos was from a guy that was using a laptop (older MacBook, IIRC) and his internal speakers just weren't reproducing the bass parts well enough that he could hear.
Also, I think he might've been a little confused over the difference between the computer "master" volume and the volume control in the video player software (both often work independently). Nevertheless, once he put headphones on, he heard everything fine.
Any chance that any of these issues might apply to you? Let me know, and we'll go from there. Feel free to PM me if you like.
Thanks!
Rob Wren
webmaster - ToddJohnsonMusic.com