4 K Q noise pebbles in a can

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My guess is the exhaust.
I think mine does it but its not that loud.
Vibrations from load and near stalling, I think.
Loose Cat innards, broken hangers?
Just a guess - Scott in BOSTON

On my 4kq there is a noise i cannot figure out anyone's help would be great.

When I let out on my clutch in 1st gear from a stop and let the engine rpm
fall below 800 rpm i get a "pebbles in a tin can" rattle.  At first I
thought
replacing the water pump would get rid of this because at normal idle i
could
hear the sound constantly.  After replacing the water pump the sound went
away at normal idle and found that the water pump had bad bearings. I did
overtighten the new water pump tension were the belt could only twist just
45
degrees instead of 90 degrees. I went about 250 miles on the tension until i
slacked the belt to the approved 90 degrees.  Did the tension kill the water
pump bearing?    However the sound now only occurs now when you let out on
the clutch in 1st gear still.
What else could be?  Clutch?  Another Water Pump bearing shot?  Engine
knock?
 Help!!