Music plays slower when booting without a GD-ROM Drive

[yhuangnic]

I added a microSD to SD adapter to the serial port of my Dreamcast and I also soldered an IDE connector. I also added a second BIOS to boot into Dreamshell v4 without a GD-ROM Drive, however, I noticed that the startup music sounds really, really slowed down.

It is not only the startup music but ingame music too. So far, I've only tested Crazy Taxi 2 and Resident Evil 3 from SD and every sound is really slow. When I reattach the GD-ROM Drive and turn the Dreamcast on again, everything sounds normal again.

Is this normal behavior or is there something wrong with my Dreamcast?

I uploaded a video to youtube showing the issue.
https://youtu.be/9SAHSsbltkY