Hey all, new to the forum. I have a 2011 with a groaning sound under normal acceleration, but when I put the pedal down it sounds fine, and then when I let off the throttle at all I get a farting noise. All started after the dealership replaced my engine and manifolds. I'm leaning towards bad blow off valves, but wondering if anyone else has a better idea. I did bring it into ford and had their "master mechanic" go for a ride with me and he was no help. He claimed it was all due to my cold air intake but that's deffinately not it because I swapped the stock air box back in and nothing changed. Any ideas would help. Thanks.