Rattle under engine at low idle

At low idle, there is a metal-on-metal rattle sound located beneath the engine. This occurred after using a hand-held wand washer that sprayed water forcibly downward between the "wall between the engine and the car interior." It is suspected that "something like a heat shield" was knocked loose. The rattle occurs only when idling low then when I "step on the gas" the rattle disappears. Previously (within the last year) the '"muffler and/or tail pipe" dropped off and dragged on the ground. It was reattached with a metal wire by hand. Without putting the car up on the rack. Casual observers have stated things like "alternator", "serpentine pulley", "engine lifters" etc. I know the "rattle" is not any of those things because of the nature of the "rattle". Ironically mechanics "insist" that they will only "put the car on the rack without me being present to witness the findings" and they will tell me what they find. This is suspicious because "I have been ripped off by auto mechanics numerous times" (i.E. Taken advantage of because I am a woman) and have been "charged for services not rendered many times" by unscrupulous auto mechanics, "at least four times in the past four years." Recently, an unscrupulous mechanic claimed to have examined my car to estimate for "placement of a horn button" rather than opening the steering wheel and repairing the horn. He told me it would cost $150.00 to $175.00 to place a horn button (if I provided the parts) a task that would take only thirty minutes. During the "examination" the mechanic "messed with something" causing a problem with my electrical system resulting in a "beeping" sound for about 30 to 45 seconds each time I start the car. (I.E. The horn dysfunction was caused by a previous mechanic who charged me $258.00 to "tighten the wobbly steering wheel". After which he claimed that he did not cause the horn dysfunction. I need to find an honest mechanic. Can anyone advise?