Engine Noise

Hi I am new to the forum and new to owning a mustang. I finally have gotten my fox convertible it is a 91 GT with alot of mods, including a vortec super charger. i ahve waitingf one for a while all the mods were bonuses. So here is the issue. Last eveing I was driving not getting on it at all and I began to hear what sounded like and exhaust leak after driving over a set of railroad tracks, car began to sound like a steam engine. I was 4 miles from home, got it back in the garage and found the first plug on the drivers side of the motor to be loose (hand loose). Took the plug out, it is definately fouled. I was able to tighten the plug without the feeling of cross threading or that. Started the motor and still sounds like a steam engine. It sounds like it is comming fromm the header area. I picked up a new plug and will be checking the header bolts when i get home tonight. I am just looking for any suggestions out there on what else it could be. Coolant is good, no smoke from tail pipes and oil is clear on the stick which was just changed 300 miles ago. I am open for any sugestion. If all else fails off to the mechanic. Thanks

Thanks guys for the suggestions. I just got home form work. All other plugs are tight. I did find 2 bolts to the header on the drivers to be loose and all the other bolts to be tight. So plugs have been replaced and all other header bolts are tight. This is where I thought the leak was coming from, we'll see tomorrow when I fire it back up. Thanks again.

I ran the car today, did not hear any leaks, but was thinking the same thing, so I am going to replace the gaskets over the winter to be safe. Does anyone know if there is a torque setting for the header bolts. I have GT40 heads. Or is this just going to be one of those maintance items that I am going to have to keep up on. Other wise car is back to normal. Thanks for the help.