Audi a3 2006 radio works but speakers don't - A3 Audi Cars & Trucks

As long as the radio is on the mic is the radio speakers. Just be sure the radio is on and it will work fine.

Reset radio Audi TT
Use the station buttons 1 through 4 to input the radio code. Press button one repeatedly until you arrive to the correct number (once would be one, twice would be two and so on.) Once you have entered the correct code in the display press the P.SCAN and RBDS simultaneously again, holding down until SAFE is displayed.Apr 24, 2014 https://www.prestigeimports.net/audi-radio-codes-a-complete-guide-from-prestige-imports

I would think the radio unit is defective or the USB wiring is at fault.

you may need to go through the menu on the radio/stereo & check if the fader is on just the front speakers, then turn it the other way to bring in the rear speakers, just like left & right balance

NO SOUND FROM ALL THE SPEAKERS OR THE REAR ONES?IS THERE A SUBWOOFER INSTALLED?NEED MORE INFO!!WHAT IS THE RADIO U HAVE ON?

Sounds like you would like to know how to get a radio code because you're locked out of your MMI?
If so, try entering your VIN here and generate your code. If that doesn't work you'll have to take it to the dealer:
http://www.radio-code.co.uk/audi-radio-codes.html

Here's a video with fuses location in Audi Q7:

try connecting them to a small radio or tape player to see if they still work ?? if they appear to work ok on a small set then i would be inclined to check the colours on the speaker wires then rmove the radio and try connecting another known to be good speaker to the output on the radio and if that works ok then renew the feed wires to rear speakers because thats where your fault would lie for whatever reason like a mouse got in or seat crushed the wires or whatever

sound like a speaker wire is grounding out somehow