Engine noise?

[64dartgt]

My rebuilt 340 engine (2500mi) was making a thumping sound...kind of like someone taping on an inverted 5 gallon bucket.  My usual mechanic said he thought it was a bad bearing.  I took it back to the engine builder.  He didn't think so, but without a lift he really couldn't get under the engine to diagnose it.  I went back to my usual mechanic who showed me that the noise is clearly being transmitted through the oil pan.  The engine builder recommended an experienced classic car mechanic that he knew pretty close to my home.  I took the car there last week.  He put the car on the lift and listened to it.  He thinks it is either the oil pickup drumming on the pan or perhaps the fuel pump.  He wants to go through it next week.

Any thoughts?

[tan top]

  is the  noise there all the time even  when idling ?
 does it increase with engine speed ?
or only appear at a given engine speed  , example !! say from 2 thousand revs up when reving  , if so have you got a mechanical oil pressure gauge !  when noise happens does the oil pressure drop any  ?

[cudaken]

My rebuilt 340 engine (2500mi) was making a thumping sound...kind of like someone taping on an inverted 5 gallon bucket.  My usual mechanic said he thought it was a bad bearing.  I took it back to the engine builder.  He didn't think so, but without a lift he really couldn't get under the engine to diagnose it.  I went back to my usual mechanic who showed me that the noise is clearly being transmitted through the oil pan.  The engine builder recommended an experienced classic car mechanic that he knew pretty close to my home.  I took the car there last week.  He put the car on the lift and listened to it.  He thinks it is either the oil pickup drumming on the pan or perhaps the fuel pump.  He wants to go through it next week.
Any thoughts?

I have never had a LA motor, but I guess the oil pump bolts could be backing out? 

If it is a automatic check the flex plate bolts. I would all so check the bell housing bolts as well. I had some bell housing bolts back out off my 68 Road Runner one time and I thought I lost a bearing in the 426 Max Wedge. After I started to pull the motor I found the lose bolts, tighten them back up and problem was gone. 

Cuda Ken

[Cooter]

You say rebuilt......I assume your builder built it? Sounds like a main bearing thump from what you describe here.

[68 RT]

I had the same noise on a 66 Pontiac. It was the fuel pump.

[Challenger340]

You say rebuilt......I assume your builder built it? Sounds like a main bearing thump from what you describe here.

yep, mains make more of a "thumping" than a "knock".  What's the Oil Pressure ?

[64dartgt]

Checked the flex plate bolts already and they are fine.  Put an oil pressure gauge on and it pressure was fine, 50 at idle and 70ish at higher rpm.  Sound ins't obvious when cold but is readily apparent once it warms up.  Can't really hear it at faster than an idle.  Definitely can hear it when coming from the oil pan, which makes me thing tranny related issues are unlikely.  Can be a little intermittent (skips beat occasionally).  The mechanic is going to pull off accessories until it perhaps goes away.  He says he can even pull the fuel pump and the oil pan to see if there is any shiny spots on it inside.