Evenexchange

For the longest time, everyone I know who owns a mustang with 30,000+ miles on it has complained about that "thud" sound that comes from underneath the passenger seat once the car is warmed up and at a stop.

What is this sound? I've heard that even the police crown victoria's do this too. I've also heard that NOBODY knows exactly what this is because it's pretty much impossible to diagnose because it happens at random. I could go a month of driving and it might happen twice in total.

cliffyk

I guess my brother and I are the exceptions that prove this rule--105k miles with no passenger side "thuds" on my '03, my brother has 145k on his '99 with no thuds there either...

itsdaveonline

I have 123k clocked and its happens very rarely...but generally it always happens when i engage the clutch fully and go into first gear. I have no idea what it is...It kinda feels like the tranny doin something funny. Or maybe thats just my car...idk haha

cliffyk

Oh that,

That's just normal RWD drivetrain noise that one would expect from what is basically a 1/2-ton pickup with a flashy body. I've never owned a higher powered RWD anything that didn't do that once in a while--I guess it never struck me as unusual...

Hangwire

2003 GT with 78,000 miles no thud.

smitty2919

I think I know what you are talking about. My 04 GT with 44K mi on it will do it randomly. I think I have found that if I turn the heat on it will make a "thud" like something hit the floorboard or something. Again very randomly and not all the time. I have heard it on my buddies 04 Mach 1 as well.

Evenexchange

Yeah, you all are talking about the same thing I am trying to describe. Nobody really knows what it is. So what is this effect that comes from a 1/2 ton pickup with a flashy body, cliff? What is actually happening so that I can fix it?

cliffyk

That's the vacuum actuated diverters and flaps/doors in the heater. Maybe that's what the OP was referring to as all Fords do it--however there's no "mystery" associated with it that I am aware of?

cliffyk

If you are referring to the thud the heater makes when you change an airflow setting, or shut down the engine, then there's nothing to fix--that's just the way it works...

If you mean the drive train noise (which is more of a clunk to my ear), and all of these are OK,

• transmission output bushing
• worn tranny output shaft, front driveshaft yoke
• worn U-joints
• bad bearings and/or gears in the rear-end
• worn spider gears/splines in the carrier

then there's also nothing to fix, it's just the way it is. High torque RWD vehicles do that...

Hangwire

When I have my fan on at all it makes a repeated "clicking/rattling" noise big time through the vents. More and more as it gets older. When I have the heat on theres a loud, crisp "toking" noise that comes from the windshield defrost vent specifically. Never did this initially @ 50,000 miles but when it first started I FREAKED out on the highway thinking it was a massive missfire. Pulled to the side of the highway and screwed with things until I realized it was when the heat was on. The only way to describe this noise is a "toking" or a smooth "pop" noise. It is still there initially when you turn the heat off but tapers off. I can definitely capture this sound on video its distinctive and its funny sounding.