Quote:
Originally Posted by lkh5650
it was hard to tell... It was periodic, every 1 second or so, very loud knocking sound and in between the period the sound was still there but not as loud/pronounce
I didn't feel extra vibrate/shake
I think it was coming from somewhere between mid center to back center of the car..
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I would check the front end for missing plastic fasteners and or bolts. In particular the 3 center plate/guard fasteners. If the 3 center points are not present - the cover will bounce against the under engine frame and resonate to the mount points sounding like middle of vehicle.
If it's aftermarket under shield - get some heavy duty fasteners that hold the center - 3 of 'em. (AutoZone Medic Isle - package of 4 is what I saw)
If you only have the outer edges of the plastic under shield or aluminum shield fastened and not the center - my friend - it's gonna bounce against the sub frame. I learned this after doing my first oil change and thinking I was slick by leaving the 3 fasteners out for "next time...."
Got to 80mph on a toll road here and thump thump thump thump..... then when I slowed down thinking WTF???? it stopped. After the second day of the same sound, I put the center 3 back in and have never heard the thumping since....