Hi there, first post here, something is bugging me from a bad experience at a Oil Can Henry's, made worse by a horrible loud sound that seemed to come from the back undercarriage of my 02 Elantra GT after pulling away from the oil change.

The sound happened twice, shortly after each other, but hasn't happened since.

CAUSES?
My worry are two little things the workers forgot. A missing light bulb, and a missing screw.

MY VISIT:
I was due for an oil change, but I mainly wanted a dead headlight fixed right away, on the left side, in front of the battery, covered by panels and bad access. I had a bulb, left over from the last headlight replacement, though, later in the process I learn I accidentally brought a brake light I also had.

ALL FOR NOTHING:
Anyway, the two employees remove 3 screws with large washers to lift a panel attached to the front of the car body, or headlight. They set the screws on part of the engine, and my bulb. They literally were pulling and tugging to detach the entire headlight assembly to access the bulb. (They have you sit in your car while they work). I'm worried they'll knock over the screws. They already finished the oil change.

NOT A DEAD BULB?
Well, they finally notice I brought the wrong bulb, no problem, they sell new bulbs, but before doing so one said the light came on, maybe it was electrical issue, moving things might have got it working for a bit. They put it all back and I was on my way. I totally forgot to get back the brake bulb.

IT HAPPENS:
As I pull out and make a left, a little ways down I hear and feel the loud banging happen under my car. I thought I hit something, but it happens again shortly after I know I never drove over anything.

WHAT'S MISSING:
I reach work to check my light and sure enough it wasn't working. I double checked the engine and noticed one of the screws and washer was missing. They most have lost it in the engine.

CAUSE OF SOUND?
Could a bulb and screw fallen into the driver side of the engine cause the loud clanking sound under the bottom middle of the car?

THE NEXT DAY:
I took it into a Pep-Boys near by for the light bulb. As I drive to there, I already started to hear a vibrating from the area where the screw was missing, around the left headlight, just another thing to aggravate me about their service. The panel was loose enough to vibrate on the body, though, not related to the clanking sound. I mentioned the whole thing about light coming on and could be electrical. They wanted to do a $80 something electrical diagnostic if what was said was true, I instead say to replace the bulb like normal. Luckily I was right, the bulb was dead, the new worked fine with no odd electrical issues. I also picked up a new screw to secure that loose panel now.

I MENTIONED THE SOUND FROM UNDER THE CAR:
I also told them what happened as I left and they said they'd take a close look under the car. They didn't find anything, or really say anything, except they handed me the missing bulb that the oil people forgot to hand back, it was shattered and found in the undercarriage.

SO AND ALSO:
Could a loose screw with large washer (quarter sized) and bulb fallen into the engine make such a disturbing sound from under the middle of the car? Also, in the last month, a new issue I have is a creak from the rear suspension (hitting bumps, or even acceleration forces) Could the loud sound have anything to do with this new creaking sound that started months after? (The car only has 27k miles)

Thanks for any thoughts