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Rattling or irratic knock from back side of engine

by Michael
(Chattanooga TN)

'91 corvette zr1- So Im working on fixing some all around issues as a new one starts. As im accelerting I do not hear the noise, but if I let off that accelerator at all there is this clacking sound. I got the oil changed, it seemed to dull it down a bit. Ive got some ideas, but havent got any real solid guesses yet. Check engine light is coming on. But it being OBD1 that doesnt tell me much.Doesnt seem to be effected by the clutch or transmission.
Cat converter going out?
loose timing chain?
loose exhaust hanger?

In working on the tune up but id hate for this thing to really break before I even get it completed.

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Jan 19, 2019
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starstarstarstarstar 		knocking in rear of engine NEW
by: Anonymous

I had that problem, sounded like a can with rocks in it. finally went to you tube for answers. rattled really bad at idle. problem was my cat. converters ,what i call is the honeycomb, was loose due to being hammered on by a mechanic to get the exhaust loose. with the car running and on ramps, rap on the cat. with a rubber hammer to see if the noise stops or changes for a couple seconds.
Aug 30, 2018
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starstarstarstarstar 		Engine noise NEW
by: Phil

I am having the same problem with my 1998C5. Mine only occurs on acceleration or when stopped on a steep hill. After I reach a higher speed it stops.I think mine may be the water pump with a piece of metal loose inside but I just can’t be sure. I do have a small amount of coolant leak is coming from the water pump area. I have looked under the car several times cannot locate it. Everyone including myself agrees it’s coming from the engine compartment. I have an appointment on September 5 with Buyavette in Atlanta to locate the problem.

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