rumble under gas petal

[srvblues]

Hey long time no post. I have just the last week noticed a minor rumble under the gas petal causing the floor to vibrate i little.
I have a 1995 mustang GT with only a KandN filter and Straight pipes on exhaust to mufflers. When i have been noticing it is early morning and when i run around 2500 rpms and in 1st thru 3rd gears. In the morning it does rumble a little when downshifting and lower rpms. In the afternoon when it is 80 to 90 degrees i only notice it at the 2500 rpm range. I tried getting it to do it while parked but it doesn't rumble. seems to only be when driving. I have listened with the windows down but i can't hear a loud enough noise to locate it. I am thinking exhuast leak but why wouldn't it rumble while parked and reving the engine to 2500 rpms??? I can't imagine it being my manual transmission. it is not a metalic rumbling more like something is against the floor board vibrating it at certain rpms. just give me ideas.

planning on new intake, cam, heads, headers, throttle body( like I need to tell u that) need the cash though.

[srv1]

first off COOL NAME!!
it may be where you joined your headers to the muffler pipes. it may be leaking only when you have it in gear cause you are putting a load on the motor and it is twisting. i would check your exhaust thoroughly. let us know.