One stereo channel gets blocked.

Can anyone help?
My Bold 9900 is an independently unlocked model (made in Mexico) since I travel and wanted to use several SIM cards according to the countries I visit. In the US I use an AT&T SIM card. (One of the reason why I bought it was because in my Curve I had the Bridge problems with the Playbook and also had the BB Maps blocked by AT&T)

I am having a problem with the Bold 9900 that it blocks one of the stereo channels. When I upgraded the OS I got the two channels working once again and I thought that I had found the "solution", but when I have to reboot or make a battery removal, the stereo channel gets blocked once again. Initially I had the version 353 and now I uploaded and installed the 440 (since it is the "official" used by AT&T). I will install the 540 version hoping that it will increase the battery life. But what is still "bugging" me is the issue with the blocked Stereo channel.
One again, can anyone offer any help?

:(

I had the same problem. I troubleshooted night and day, and found it was a slight glitch in my desktop manager software.
When I "back up" all the info from phone to my Mac, then "restored" all, as soon as I did a reboot on phone, I would lose sound in one channel. Drove me nuts, I thought it was new apps I was downloading. This went on from day. Even sent my phone in for repair, but brand new loaner did same thing, first time rebooting.
If I just pick and chose which items to "restore" (email, address, Cant temember which others, just the basics) it was fine. I then deleted bb desktop manager, then reinstalled, and no more prolems. Even when "restore all"
Hope this helps.Let me know.

I thank you for your comments. I tried your advices as well and the results keep being much the same.
I believe it is a glitch of the models we both have and I hope that the "new" upgrade that they say will come from RIM will solve this matter.
The only solution I found is to constantly do an "upgrading" (that is, re-installing the OS) with the BDesktop Software after doing a reboot (or removing the battery) and finding that the stereo channel is once again being blocked. This is frustrating indeed, but it is the only solution I have found for the moment.
Like you, this is my second BB Bold 9900 with the same problem (both made in Mexico).
I am with AT&T and I wonder if the models they are offering now are all made in Mexico as well and if they would face the same problem!
If I had a chance I would try with one made elsewhere, for example in Hungary. Otherwise, I am very satisfied with the 9900, especially the keyboard! And also to discover that the touch screen is becoming "addictive".