Joel, Thanks again for responding. I will pull the sending unit out. I believe I can pull the unit out from the fill cap area on this year of Vette, so at least I wont have to drop the tank. I will verify that procedure before I begin- as the memory isnt as it once was. Jon

Dang, you're right.  Didn't think about the rubber hoses. 

I will let everyone know what I find out on this issue. I am setting aside some time on Sunday to check into it. If there are any other ideas or suggestions, please pass them on. Thanks Jon 

Sunday May 4th.......OK, here is the story. Ran the vette for half an hour. Gas level at 1/4 tank. After reaching operating temp, ran high idle (55mph equal) for 1-2 minutes. After idle went to curb, rat a tat a tat started up again in the right rear. Put the long screwdriver to the surface of the fuel pump and no abnormal noise at all. Sounded good. Removed the fuel cap and issue did not change. I pressed the screwdriver on the fuel lines riding on top of rear frame arch and positively pinpointed the sound. Plain as day, rat a tat tat , loud and clear. Lines running toward bottom where the rear dog leg meets the straight run of the frame were quiet. So, something is affecting the fuel lines from appx a 2-3 ft run from the fuel tank until they make the slope down the right rear dog leg. Supply line was cold to the touch and a fuel return line was allowing a steady stream of fuel back to the tank. The only two things I can think of are- as previously mentioned, something collapsed with the fuel sock (I looked in the tank through the fuel fill hole but all looked normal) or some kind of line shock is happening or combo of both. The only time this has done it was when the fuel level got this low. When I bought the car and drove it home, there was 3/4 of a tank of fuel and never had the noise. Drove it a couple of more times before this noise started appearing which was just about the 3/8th area of the fuel gauge. So, at my wits end. Any ideas? ?  Thanks Jon 

|UPDATED|5/4/2014 3:02:33 PM (AZT)|/UPDATED|

Ok everyone, need some opinion input. I think I have narrowed down what is causing this noise. It has to be air getting into the line somehow. Since the car is bone stock original, I am assuming that maybe the rubber hoses are dried up and the clamps are weakening. I dont believe it is the sending unit, fuel pump or fuel pump drive rod. I believe it is time to replace all the original rubber connection hoses and the original clamps. I hate to do this as I want the car as original as it was from day one, but I like driving my cars so- its a love hate thing. Any suggestions are much appreciated. Thanks Jon

see if you have brake dust covers and see if they are hitting the brake caliper mine does this and it hits in certain areas only !! I pushed on the  the cover a little bit were you can see scratch marks on the cover where it hits the caliper very little clearance and it made a rat tat noise that was driving me crazy !!! from the right rear. Sometimes it's just something stupid it fixed the noise but cam back a month later had to push on the covers again and noise is gone !! 

Thank for the response. I dont have caliper covers. I had pinpointed the noise at the rear area of fuel lines. After meeting up with a couple of mechanic buddies this past Saturday, we all came to the conclusion that air maybe getting into the fuel line somehow. The noise and the pulsation action felt on the line is equal to getting air trapped in a water line. Anyway, since this past Sunday was a "no work in the garage day" I will tackle the issue this week. Any other ideas are appreciated. If I am off my rocker on this, let me know ! It is one of those issues that doesnt happen often enough to generate any history from someone. Thanks again. Jon 

Ya, Jon I got one of those "mystery" problems also.  Mine is that the drivers window does not want to go up and down sometimes.  I have checked the window switch and I have followed all the wires through the door and to the motor but I cannot find a problem.  I have power at the switch and also checked for continuity.  JOEL!!!  HELP!!