Heres my setup: 2003 Tahoe with Bose. I replaced the front speakers with a component set that is amped, but I want to keep the rest of the Bose speakers including the sub. I bought a Bose Module. After I plugged everything up, the Bose amped speakers are WAYYY louder than my amped speakers (with the gain on the amp all the way up). There is also some bad-ground-ish noise coming thru the speakers. Has anyone else experienced this with a Bose system?

How can I lower the output level of the Bose amp? I read in another thread that before you take the stock head unit out, you should balance bass/treble .. this sounds silly, but is it true?

Please give me some advice!

It may sound silly, but with the blose system it's true.

Also, make absolutely sure that you are using a Bose-designated interface, not just a class-2 databus interface. They look identical, and will work in lieu of each other, but the gain differential (read : volume) and equalization will be different. In PAC products, make sure you are using an OS-2BOSE, not just an OS-2. In Peripheral, a GMAH-24B, not a GMAH-24, etc.

I also have a 2003 GMC with the Bose system with all factory speakers. I have terrible humming also. I tried new grounds but didn't make a difference. I'm not sure what interface I'm using though.

FYI, there's more than just "Bose". You need to identify if you have Premium (Lux) Bose or Standard Bose. Standard Bose uses front AND rear speaker level inputs, whereas Premium Bose only uses front speaker level inputs. If you don't require a chime module, you likely have Premium. Don't know if attempting to hook up rear speakers on a Premium Bose would cause issues...

Also, you MIGHT want to try adjusting the volume through factory head unit higher/lower before disconnecting it. Since base, treble, fade, and balance are stored in amp post factory disconnect, it's possible spacial effects and volume level are stored as well - not sure, but before plugging my AVIC I set volume to max, treble, base, fade, and balance to neutral (centered).

Worst case, I imagine you could hook up a gain control to Bose to regulate it equal to your aftermarket amp. Humming though I couldn't say. In my experience, bad sound and video always came back to poor, faulty, or wrong connections...