Re: strange sound when I step on the gas
What did the shop include in the tune up? Is the engine light on?
Without knowing what this sound sounds like, it could be either the fuel injectors just doing their job (Dodge vehicles are known for loud injectors), but I didn't notice it in the Focus I had as a rental for a few days last year. The other more serious side is that you might be experience the sound of engine knock, or ping. This is when the fuel/air mix detonates before the piston is at top dead centre, and can create damaging effects if not taken care of. Knock sensors built into the software program should solve that. However, try putting in 4-5gallons of 89 or 91 octane fuel to see if the sounds goes away. Make sure you have very little regular gas left in the tank to get a proper test done. If the sound goes away after using higher octane fuel then it is pre-detonation and the knock sensors have failed.
Another possible solution is that the idler pulley is shot and needs to be replaced. The bearings in the pulley should last the life of the vehicle - but not always. With the engine running, open the hood and make sure the belt is running straight and true. A more involved way to check is to take the belt off the idler pulley and try to rock it back and forth and if there is play, then you know its shot.
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!