Hi and welcome :)
Difficult to say on the sound without hearing it. If it actually sounds like something sliding back and forth then perhaps it could be just that, albeit something out of site?
I'd try to isolate the area that it's coming from first. Once you have done this it may be a case of taking trim apart to try and find the culprit...
00665 - Boost Pressure Regulation: Control Range Not Reached
Possible Causes:
- Hoses/Pipes no fitted correctly, disconnected or leaking
- Charger Pressure Control defective
- Faulty turbo (hopefully you can ignore this one but you never know)
- Faulty Diverter Valve
Possible fixes:
- Check all hoses and pipes are connected correctly
- Check/replace/clean Charge Pressure Control
- Check Turbo again
- Check Diverter Valve
00125 - Trigger for On Board Diagnostic Lamp; Malfunction