Re: Door Chime, Turn signal noise
Unfortunately there really isnt a simple answer to your question. The solution is going to depend on what harness/interface they used when they installed it, and exactly how it was installed. The 2 that I am most familiar with are very different in how they function.
The first, and probably most similar to the other interfaces on the market is the unit made by Metra: GMOS-LAN-04. If they used this, or another similar unit, the chimes are designed to retained thru the left front speaker just like the factory radio. Any time I have used it with an upgraded stereo and no amplifier, I have never seen any issues with it being too loud, and the volume can be adjusted. The only time I have seen an issue with it is when hooked up thru a 4 channel amplifier. The amplifier tends to overly amp the chimes and clicks. The only solution I have seen is to turn down the gain some, but this is not usually the best solution for sound quality, as the gains should be set to match the audio system. Unfortunately this is the more common style harness used in Malibus because it is the style that will retain OnStar.
I used a different harness on my personal vehicle because I did not want to retain onstar and knew I would be adding a 4 channel amp. The one I used is made by Scosche model GMLAN13SR. The advantage of this unit for this situation is the chimes are played thru a small speaker on the harness module itself, so are independant of any amplification. This means you can use whatever power levels or settings you want without having to worry about it making the chimes and clicks too loud. I believe the PAC brand interface functions the same way. Again the only downfall of this type of interface is that it will not retain OnStar.