I've had a similar problem. Only on my 1st Hero, but the left channel went out randomly today. Thought it was a headphone issue, bought new ones, it wasn't. Checked the old and new headphones on other devices, they work. Definitely the 3.5mm jack on the phone.
What did you end up doing?
I'm not thrilled with getting another Hero, even though I have insurance. Does anyone have any advice or suggestions? I use my music through headphones a ton, so before I go back to school, I need this fixed. Guy told me he'd order a new Hero for me, could send it to my school... ugh. Any ideas?
Sprint Samsung Galaxy S III
ROM: Vanilla RootBox | v3.9.1 (May 8) | Jellybean 4.2.2
Ktoonsez KT747-LJ7 | v13.2.20 (Feb 20) | Linux 3.0.65
Recovery: TWRP | v126.96.36.199 (April 8) | Holo-Light Theme
SD Card: PNY | 16GB | Class 10
History: Kyocera 7135|Blackberry 7250|HTC Apache|HTC Mogul|HTC Touch Pro|HTC Hero|HTC EVO 3D|Samsung Galaxy S III