From the Ibus Facebook group wiki:
“No sound after radio installation
After installation of the radio is garkein sound [ edit ]
Check if you have a power amp left in the boot.
If so, there are really only two options:
The power amplifier does not receive a switch-on signal ("remote") or voltage.
It is DSP installed and you have either no DSP license to the I-BUS app purchased or no Resler USB flash drive AND no license.
There is a coding error of the DSP. This problem can only be solved by a capable coder.”
I’ve also read in post on there, that the usb stick can sometimes throw out the coding for DSP. Perhaps this is why you lost your 20 seconds of sound?

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Current vehicles
2001 325XI
2006 X5 3.0
2004 X5 3.0