As long as the central locking system is unlocked the trunk is unlocked and the button to open the trunk is between the tag lights. So a extra button inside to open the trunk is unnecessary. If the car is locked the button won't work. The valet lock button is so the trunk won't unlock with the centr...

I have a 2004 V70 and installed a similar Yatour device. Mine has the addition of the USB port but is otherwise like yours. I've not had any noise issues. I have the VOLVO factory issue coils.

I had this whine in my T5 and then my kids told me it was Taylor Swift

Solder black wire to the GND wire in the cable. The idea is to feed the +12v through the noise suppressor.

When I was a kid, it meant Rat Fink. I think he's referring to radio frequency.