Loud clicking noise under hood when in idle but in gear

Since I had my oil changed (and whatever else Jiffy
Lube checks during the process) a week and a half
ago, I've noticed a really loud clicking noise
underneath my hood and it is only when I am in idle
but my car is in gear especially when my AC is on it
typically stops when I accelerate. I have taken it
back to Jiffy Lube twice one time didn't do
anything the second time I had them at least look
under the carriage and look under the hood and
they could not find anything however it look like the
other battery cover was loose or the forgive me the
part that goes over where you change your oil I
guess we'll your spark plugs are that cover was
loose or I'm also read that it could be my axle