Greetings from Scotland. I purchased my 05 GT Auto in April 2010 and for the first 12months of ownership, she roared. This was my first V8 and the noise generated justified my choice and I guess, the stupid cost of fuel over here. She is fairly standard, other than a C&L and SLP exhaust. I should add that the engine check light was on from day one. Despite not having a reader, I was assured that this was due to the car running lean due to the C&L or SLP's(or both indeed). I have no reason to believe that the car had been tuned prior to my ownership. She sounded awesome, regardless of the speed. At times you were hanging on for dear life-I'm sure you folks know what I mean! Anyway, a year past April I needed a new battery. From the minute that battery went on, the car sounded garbage and lethargic. The roar went and really everything seemed like an effort, especially at low revs. Before,if you rev'd the car there was a roar/crackle/pop. Now it sounds more like a household "Henry The Hoover". The roar was replaced by a deep "farting" drone and despite everything I've tried, the frustration continues to this day. Oddly enough, at speed, say 70+ the noise and response is still pretty good and kick-down works fine. The battery was the correct one so I don't think that is the issue though I'll say again, the car was awesome until that day. I've done the idle test more times than I care to mention, the mass air sensor has been cleaned several times and the throttle body has been cleaned and now just this weekend been replaced. That didn't work either!! The car never came with a reader, so I got a Diablo Predator. I tried the canned tunes and they seemed to help but the deep farting drone still prevails.I appreciate that SLP's can drone at highway speeds but this is something else. I managed to get the C&L tuned in but I reckon the car sounds worse. Returning the stock air box makes no difference. Why have I lost my roar? Why does the car feel lethargic?I have no engine codes so I guess nothing major is wrong and fuel consumption is as it should be. The car is well serviced, fuel filters etc, but nothing seems to work. Ideas please. Thanks in advance.