Wanted to pass this along for those that have experenced the same problem that I was having.

I installed the RT Navigation Interface Module so I could use the ZUMO's MP3 function and have voice override for the navagation commands. After the installation all other functions worked great, except when listening to the MP3 player the unit would start to pick up false mute signals and the volumn would start to fade.
As it turns out the NIM that I installed was part number 76000024 which is an out dated module. We replaced it with new 76000024A and the fading problem is now history.
The part number was on the main wire going to the module.

 

Thanks for the info Jimmy. Getting ready to do the same thing.

 

Just completed the install of the NIM and now need to dig back into it to check my part number! But, wanted to add that after the install, it did not work as advertised - it would not mute the radio/CD/WB when the nice lady wanted to instruct me where to turn. I have a EG Classic so no speaker switch to have in the wrong position. well, problem solved. The instructions start out by saying "remove the main fuse" (also known as the "maxi-fuse"). Well, all HD instructions start out with that step and I always ignore it, as I did this time. well. before digging into the wiring again, I pulled the main fuse, waited 5 minutes (H-D says 5 minutes will cause the radio to re-boot). and lo and behold, it now works as advertised!
Also, remember to check the date on your instructions, if prior to 8-26-2010 there are two wires crossed - pin 19 and 31 in the 35 pin connector. my instructions were Sept 2010 and were correct.
Have a nice day everyone!

 

I'll be doing this soon, subscribed.