I have a 97 F150 4.6L with 130,xxx miles on it. I have had this problem for a little without much luck on finding a solution. Whenever I am towing my boat or a trailer and going uphill or accelerate or even when I just on a hard acceleration while cruising when I am not pulling anything, I get a rattling noise that sounds like a baby rattle. It sounds like it is coming from the lower driver side behind my gas pedal.
I don't run anything other than 93 octane and have ran Lucas injector cleaner or Seafoam in my tank every 6 months or so.
Here are a few things I have done to my truck, not to try and fix this problem but to fix other issues: replaced MAF sensor,DPFE sensor, EGR Valve, Coil Packs and Spark plugs. I have also had my exhaust redone from the manifolds back and did not eliminate my converters.
I was told that it maybe had something to do with my timing so I have tried with my edge programmer to: program back to stock and lower my timing and neither made any difference.
To try not to leave anything out the only other odd thing I have had happen was a random check engine light that would come on but would go off by itself
P0141: Downstream heated O2 sensor heater circuit fault(Bank 1)
P0420: Catalyst system efficiency below threshold (Bank 1)
P0232: Fuel pump secondary circuit high
Only once I had P0153: Upstream heated O2 sensor circuit slow response (Bank 2), this code has never returned.
To my knowledge the secondary O2 sensors shouldn't affect my driveablility so its never been priority to even change. I have asked about the P0232 with the response that its not a problem which doesn't make sense otherwise I wouldn't have a check engine light.
Any suggestions?

Thanks in advance

 

check your exhaust manifolds. see if you see any nuts broken off the studs. these trucks are notorious for the manifolds leaking.

 

Wouldn't I hear this at any time though? It doesn't happen if I rev it up at idle mainly when I am towing and accelerate. I'll take a look though.

EDIT: All the studs look fine, a little rusty but all in tack.