2005 noise on acceleration

[apachechas]

I have a 2005 convertible with 20,000 miles on it. Recently I stopped for gas and after filling up and leaving the station I noticed a noise when accelerating in first and second gear that sounded like pre ignition knocking. I assumed I had gotten bad gas. However after several tanks of gas I get the same noise and am begining to wonder if it is a transmission issue. There is no vibration transmitted to the shift just the noise.

Anyone had this issue?

Thanks, Charlie Stuart
cstuart@cesllc.com